Geometry Terms List
Geometry vocabulary is the foundation of every geometry course. Without knowing the precise meaning of terms like congruent, perpendicular, or supplementary, it is nearly impossible to follow proofs, solve problems, or communicate solutions clearly. This page collects the most important geometry terms and definitions in one place — from basic angle relationships and triangle properties to circles, polygons, area, and volume. Whether you are studying for a test, reviewing for the SAT, or just need a quick refresher, use this list as your go-to geometry vocabulary reference.
Key Concepts
An angle is the figure formed by two rays sharing a common endpoint (the vertex), measured in degrees or radians.
Two figures are congruent if they have exactly the same shape and size, so one can be placed on top of the other with a perfect fit.
Parallel lines are lines in the same plane that never intersect, no matter how far they are extended in either direction.
Perpendicular lines are two lines that intersect to form a right angle (90 degrees).
The Pythagorean Theorem states that in a right triangle, the sum of the squares of the two legs equals the square of the hypotenuse: a² + b² = c².
The area of a triangle equals one-half the base times the height, giving the amount of two-dimensional space the triangle encloses.
The area of a circle is found using the formula A = πr², where r is the radius of the circle.
Volume is the total amount of three-dimensional space enclosed within a solid figure, measured in cubic units.
Similar figures have the same shape but not necessarily the same size — their corresponding angles are equal and their corresponding sides are proportional.
Symmetry is a property of a figure that can be mapped onto itself by a reflection, rotation, or translation.
Two angles are supplementary if their measures add up to 180 degrees; they often appear as a linear pair on a straight line.
Surface area is the total area of all the outer faces and curved surfaces of a three-dimensional solid, measured in square units.
All Geometry Terms List Terms (31)
- Acute Angle
- Alternate Interior Angles
- Angle
- Angle Bisector
- Area of a Circle
- Area of a Triangle
- Circumference
- Complementary Angles
- Congruent
- Diagonal of a Polygon
- Diameter
- Distance Formula
- Equilateral Triangle
- Hypotenuse
- Isosceles Triangle
- Midpoint
- Obtuse Angle
- Parallel Lines
- Perimeter
- Perpendicular Lines
- Polygon
- Pythagorean Theorem
- Radius
- Reflection
- Right Angle
- Rotation
- Similar Figures
- Supplementary Angles
- Surface Area
- Symmetry
- Volume