geometry Vocabulary
JamWise Education Team·Updated March 2026
The geometry strand is a core part of the K-8 math curriculum. It encompasses 112 vocabulary terms that students encounter as they progress from kindergarten through 8th grade. Each term builds on previous knowledge, creating a spiral of deepening understanding that prepares learners for increasingly complex concepts.
Understanding geometry vocabulary is essential for classroom discussions, assessments, and real-world application. Below you will find every term organized by grade level, so teachers and parents can quickly identify which words are appropriate for their students and explore definitions tailored to each developmental stage.
Kindergarten
(22 terms)
Above
Up higher. Over something.
Behind
In back of something.
Below
Down lower. Under something.
Beside
Right next to something.
Between
In the middle of two things.
Circle
A round flat shape with no corners.
Compose
To put small shapes together to make a bigger one.
Cone
A solid shape with a point on top and a circle on the bottom.
Corner
Where two sides of a shape meet.
Cube
A solid shape with 6 flat square sides.
Cylinder
A solid shape like a can. Two flat circles on the ends.
Flat
Smooth and even. Not bumpy or round.
Hexagon
A flat shape with 6 sides and 6 corners.
In front of
Ahead of something. Before it.
Next to
Right by the side of something.
Rectangle
A flat shape with 4 sides and 4 corners. Two sides are longer.
Shape
The form of a thing. How it looks.
Side
A straight line that is part of a shape.
Solid
A shape you can pick up and hold. Not flat.
Sphere
A solid round shape like a ball.
Square
A flat shape with 4 equal sides and 4 corners.
Triangle
A flat shape with 3 sides and 3 corners.
1st Grade
(7 terms)
Attribute
Something you notice about a shape, like its color, size, or number of sides.
Composite shape
A new shape made by putting two or more shapes together.
Edge
A line where two faces of a solid shape meet.
Face
A flat surface on a solid shape.
Three-dimensional
A solid shape you can hold. It has height, width, and depth.
Two-dimensional
A flat shape. You can draw it on paper.
Vertex
A corner where two sides of a shape meet.
2nd Grade
(9 terms)
Angle
The space between two lines that meet at a point.
Congruent
Shapes that are exactly the same size and shape.
Pentagon
A flat shape with 5 sides and 5 corners.
Polygon
A flat shape with straight sides that is closed all the way around.
Quadrilateral
A flat shape with exactly 4 sides and 4 corners.
Rectangular prism
A solid shape like a box with 6 flat rectangular faces.
Rhombus
A flat shape with 4 sides that are all the same length. Like a tilted square.
Symmetry
When one half of a shape looks like a mirror copy of the other half.
Trapezoid
A flat shape with 4 sides. One pair of sides runs in the same direction.
3rd Grade
(17 terms)
Acute angle
An angle that is smaller than a right angle — it measures less than 90 degrees.
Cone
A 3D shape with one flat circular face and one curved surface that comes to a point.
Congruent
Having the exact same shape and size. Two shapes are congruent if one fits perfectly on top of the other.
Cube
A solid shape with 6 square faces that are all the same size, like a dice.
Cylinder
A 3D shape with two flat circular faces and one curved surface, like a can.
Hexagon
A polygon with exactly 6 sides and 6 angles.
Obtuse angle
An angle that is bigger than a right angle — it measures more than 90 degrees but less than 180 degrees.
Parallel lines
Lines that are always the same distance apart and never cross, like railroad tracks.
Pentagon
A polygon with exactly 5 sides and 5 angles.
Polygon
A flat, closed shape made of straight line segments. Triangles, rectangles, and hexagons are all polygons.
Quadrilateral
A flat shape with exactly 4 straight sides and 4 angles. Squares, rectangles, and trapezoids are all quadrilaterals.
Rhombus
A quadrilateral with 4 sides that are all the same length. It looks like a tilted square.
Right angle
An angle that makes a perfect square corner, like the corner of a book. It measures exactly 90 degrees.
Sphere
A perfectly round 3D shape, like a basketball or globe.
Trapezoid
A quadrilateral with exactly one pair of parallel sides.
Triangle
A polygon with exactly 3 sides and 3 angles.
Vertex
The point where two sides of a shape or two rays of an angle meet. A triangle has 3 vertices.
4th Grade
(26 terms)Acute angle
An angle that measures less than 90 degrees. It is narrower than the corner of a square.
Angle
A figure formed by two rays that share the same endpoint, called the vertex.
Classify
To sort shapes or objects into groups based on their properties, like number of sides, types of angles, or parallel sides.
Degree
The unit used to measure angles. A full turn around a circle is 360 degrees. A right angle is 90 degrees.
Equilateral triangle
A triangle where all three sides are the same length and all three angles are equal (60 degrees each).
Hexagon
A polygon with six sides and six angles.
Isosceles triangle
A triangle with at least two sides that are the same length.
Line
A straight path that goes on forever in both directions, with no endpoints.
Line of symmetry
A line that divides a shape into two halves that are mirror images of each other.
Line segment
A straight path between two points. Unlike a line, it has a definite start and end.
Obtuse angle
An angle that measures more than 90 degrees but less than 180 degrees. It is wider than a square corner.
Octagon
A polygon with eight sides and eight angles, like a stop sign.
Parallel lines
Lines in the same flat surface that never cross, no matter how far they extend. They stay the same distance apart.
Parallelogram
A quadrilateral with two pairs of parallel sides. Opposite sides are equal in length.
Perpendicular lines
Two lines that cross each other to form a right angle (90 degrees), like a plus sign.
Point
An exact location in space, shown as a dot. A point has no size — only position.
Polygon
A closed flat shape with straight sides. Triangles, quadrilaterals, pentagons, and hexagons are all polygons.
Protractor
A tool shaped like a half-circle used to measure and draw angles in degrees.
Quadrilateral
A polygon with exactly four sides and four angles.
Ray
A part of a line that has one endpoint and goes on forever in one direction, like a beam of light.
Rectangle
A quadrilateral with four right angles. Opposite sides are equal in length.
Regular polygon
A polygon where all sides are the same length and all angles are the same size.
Right angle
An angle that measures exactly 90 degrees, forming a perfect square corner.
Scalene triangle
A triangle where all three sides are different lengths and all three angles are different sizes.
Straight angle
An angle that measures exactly 180 degrees, forming a straight line.
Two-dimensional
A flat shape that has only length and width, with no thickness. Circles, triangles, and rectangles are 2D shapes.
5th Grade
(24 terms)
Coordinate plane
A flat grid formed by two number lines that cross at a right angle — a horizontal x-axis and a vertical y-axis.
Cube
A special rectangular prism where all 6 faces are identical squares. Each edge is the same length.
Edge
The line segment where two faces of a 3D shape meet. A cube has 12 edges.
Face
A flat surface on a 3D shape. A rectangular prism has 6 faces, and each face is a rectangle.
Hierarchy
A system of classification organized from general to specific. In geometry, a square is a special rectangle, which is a special parallelogram.
Ordered pair
Two numbers written in parentheses that name a point on a coordinate plane. In (3, 5), go right 3 and up 5.
Origin
The point where the x-axis and y-axis cross on a coordinate plane, written as (0, 0).
Parallelogram
A quadrilateral with two pairs of parallel sides. Opposite sides are equal in length.
Polygon
A closed flat shape made of straight line segments. Triangles, quadrilaterals, pentagons, and hexagons are all polygons.
Polyhedron
A 3D shape where all the faces are flat polygons. Cubes, prisms, and pyramids are polyhedra. Spheres and cones are not.
Prism
A 3D shape with two identical, parallel polygon faces (called bases) connected by rectangular sides.
Pyramid
A 3D shape with a polygon base and triangular faces that meet at a single point (apex) at the top.
Quadrilateral
Any polygon with exactly four sides and four angles. Squares, rectangles, parallelograms, rhombuses, and trapezoids are all quadrilaterals.
Rectangular prism
A 3D shape with 6 rectangular faces, like a cereal box or a brick. Its volume equals length times width times height.
Rhombus
A parallelogram with four sides that are all the same length. A square is a special rhombus with right angles.
Solid figure
Another name for a three-dimensional shape. Solid figures have length, width, and height, unlike flat shapes.
Three-dimensional
A solid shape with length, width, and height. Cubes, spheres, and pyramids are 3D shapes — they take up space.
Trapezoid
A quadrilateral with exactly one pair of parallel sides.
Two-dimensional
A flat shape with only length and width and no thickness — like a drawing on paper. Circles, triangles, and rectangles are 2D.
Vertex
The point where two or more edges of a 3D shape meet, or where two sides of a polygon meet. A cube has 8 vertices.
X-axis
The horizontal number line on a coordinate plane that runs left and right.
X-coordinate
The first number in an ordered pair. It tells how far to move right or left from the origin on the x-axis.
Y-axis
The vertical number line on a coordinate plane that runs up and down.
Y-coordinate
The second number in an ordered pair. It tells how far to move up or down from the x-axis on the y-axis.
6th Grade
(14 terms)
Area
The number of square units that cover a flat surface without gaps or overlaps. Area is measured in square units like square centimeters.
Compose
To put two or more shapes together to form a new shape. You can compose two triangles to make a rectangle.
Decompose
To break a shape apart into simpler shapes. You can decompose a trapezoid into a rectangle and two triangles.
Edge
A line segment where two faces of a three-dimensional figure meet. A cube has 12 edges.
Face
Each flat surface of a three-dimensional figure. A cube has 6 faces, and each face is a square.
Net
A two-dimensional pattern that you can fold up to make a three-dimensional figure. A cube has a net made of six connected squares.
Parallelogram
A four-sided figure with two pairs of parallel sides. Rectangles and rhombuses are special types of parallelograms.
Polygon
A closed flat shape made of straight line segments that do not cross each other. Triangles, rectangles, and hexagons are all polygons.
Polyhedron
A three-dimensional figure whose faces are all flat polygons. Prisms and pyramids are types of polyhedra.
Prism
A three-dimensional figure with two identical parallel bases connected by rectangular faces. A cereal box is a rectangular prism.
Pyramid
A three-dimensional figure with one base that is a polygon and triangular faces that meet at a single point called the apex.
Surface area
The total area of all the faces of a three-dimensional figure. Imagine unfolding a box and measuring every flat surface.
Vertex
A point where two or more edges meet in a three-dimensional figure, or where two sides meet in a polygon. A cube has 8 vertices.
Volume
The amount of space inside a three-dimensional figure, measured in cubic units. The volume of a rectangular prism is length × width × height.
7th Grade
(19 terms)
Adjacent angles
Two angles that share a common side and a common vertex but do not overlap.
Angle
A figure formed by two rays that share a common endpoint called the vertex. Angles are measured in degrees.
Area of a circle
The space enclosed by a circle, calculated using A = πr², where r is the radius.
Area of a triangle
The space inside a triangle, calculated using A = (1/2)bh, where b is the base and h is the height.
Circumference
The distance around a circle. You can find it using C = πd or C = 2πr, where d is the diameter and r is the radius.
Complementary angles
Two angles whose measures add up to 90 degrees. If one angle is 35°, its complement is 55°.
Composite figure
A figure made up of two or more simple geometric shapes. To find its area or volume, break it into parts and add them up.
Congruent
Exactly the same shape and the same size. Congruent figures can be placed on top of each other with a perfect match.
Cross section
The shape you get when you slice through a three-dimensional figure with a flat cut. Slicing a cylinder horizontally gives a circle.
Diameter
A line segment that passes through the center of a circle and touches both sides. The diameter is twice the radius.
Pi
The ratio of any circle's circumference to its diameter. Pi (π) is approximately 3.14159. It is the same for every circle, no matter the size.
Prism
A three-dimensional figure with two identical parallel polygon bases connected by rectangular faces.
Radius
The distance from the center of a circle to any point on the circle. The radius is half the diameter.
Semicircle
Half of a circle, formed by cutting a circle along its diameter. Its area is half the area of the full circle: A = (1/2)πr².
Supplementary angles
Two angles whose measures add up to 180 degrees. If one angle is 120°, its supplement is 60°.
Surface area
The total area of all the outer faces of a three-dimensional figure. You find it by adding up the area of each face.
Triangle inequality
The rule that any side of a triangle must be shorter than the sum of the other two sides. If a + b is not greater than c, the three lengths cannot form a triangle.
Vertical angles
The pair of opposite angles formed when two lines cross. Vertical angles are always equal in measure.
Volume of a prism
The space inside a prism, calculated by multiplying the area of the base times the height: V = Bh.
8th Grade
(29 terms)
Alternate interior angles
Angles on opposite sides of a transversal and between the two lines it crosses. When the lines are parallel, these angles are equal.
Angle-angle similarity
If two angles of one triangle are equal to two angles of another triangle, the triangles are similar. This is called the AA criterion.
Cone
A three-dimensional figure with one circular base that tapers to a single point called the apex.
Congruence transformation
A combination of translations, rotations, and reflections that moves a figure to a new position without changing its size or shape.
Congruent
Figures that are the same shape and same size. One can be moved onto the other using translations, rotations, and reflections.
Converse of the Pythagorean theorem
If the sum of the squares of two sides of a triangle equals the square of the third side (a² + b² = c²), then the triangle is a right triangle.
Coordinate proof
A way to prove geometric relationships by placing figures on a coordinate plane and using algebra (distance formula, slope, midpoint).
Corresponding angles
Angles in matching positions when a transversal crosses two lines. When the lines are parallel, corresponding angles are equal.
Cylinder
A three-dimensional figure with two identical circular bases connected by a curved surface. A soup can is shaped like a cylinder.
Dilation
A transformation that makes a figure larger or smaller by a scale factor from a center point. It changes size but not shape.
Exterior angle of a triangle
An angle formed by one side of a triangle and the extension of an adjacent side. It equals the sum of the two non-adjacent interior angles.
Hypotenuse
The longest side of a right triangle, located opposite the right angle.
Interior angles of a triangle
The three angles inside a triangle. They always add up to 180 degrees.
Legs of a right triangle
The two sides of a right triangle that form the right angle. They are shorter than the hypotenuse.
Parallel lines
Two lines in a plane that never intersect. They are always the same distance apart.
Perpendicular lines
Two lines that intersect to form a 90-degree angle.
Pythagorean theorem
In a right triangle, the square of the longest side (hypotenuse) equals the sum of the squares of the other two sides: a² + b² = c².
Reflection
A transformation that flips a figure across a line, creating a mirror image. The line of reflection acts like a mirror.
Rigid motion
A transformation that preserves the size and shape of a figure. Translations, rotations, and reflections are rigid motions. Dilations are not.
Rotation
A transformation that turns a figure around a fixed point called the center of rotation. Every point moves along a circular path.
Similar
Figures that have the same shape but possibly different sizes. Corresponding angles are equal and corresponding sides are proportional.
Similarity transformation
A sequence of rigid motions followed by a dilation. It can change a figure's size but keeps the same shape.
Sphere
A perfectly round three-dimensional figure where every point on the surface is the same distance from the center. A basketball is a sphere.
Supplementary angles
Two angles whose measures add up to 180 degrees. Together they form a straight line.
Translation
A transformation that slides every point of a figure the same distance in the same direction. The figure does not rotate or flip.
Transversal
A line that crosses two or more other lines at different points. When a transversal crosses parallel lines, it creates special angle pairs.
Volume of a cone
The space inside a cone, calculated with V = (1/3)πr²h. A cone's volume is one-third the volume of a cylinder with the same base and height.
Volume of a cylinder
The space inside a cylinder, calculated with V = πr²h, where r is the radius and h is the height.
Volume of a sphere
The space inside a sphere, calculated with V = (4/3)πr³, where r is the radius.