Geometry Glossary
25 essential terms — because precise language is the foundation of clear thinking in Geometry.
Showing 25 of 25 terms
A figure formed by two rays sharing a common endpoint (vertex), measured in degrees or radians.
A continuous portion of the circumference of a circle, measured by its central angle in degrees or by its length.
A line, ray, or segment that divides an angle or a segment into two equal parts.
A straight line segment whose endpoints both lie on a circle. The longest chord of a circle is the diameter.
The total distance around a circle, calculated as $C = 2\pi r$ or $C = \pi d$, where $r$ is the radius and $d$ is the diameter.
Figures that have exactly the same shape and size. Congruent figures can be mapped onto each other using rigid transformations.
In a right triangle, the ratio of the length of the side adjacent to an acute angle to the length of the hypotenuse.
A chord that passes through the center of a circle; its length is twice the radius.
A transformation that changes the size of a figure by a scale factor relative to a fixed center point, preserving shape but not necessarily size.
The side opposite the right angle in a right triangle; it is always the longest side of the triangle.
A transformation that preserves distances and angle measures. The four isometries are translation, rotation, reflection, and glide reflection.
A segment connecting a vertex of a triangle to the midpoint of the opposite side. The three medians intersect at the centroid.
The point that divides a line segment into two equal parts, located at the average of the endpoints' coordinates.
Lines in the same plane that do not intersect, no matter how far extended. In coordinate geometry they have equal slopes.
The total distance around the boundary of a two-dimensional figure, calculated by summing all side lengths.
A line that is perpendicular to a segment at its midpoint. Every point on a perpendicular bisector is equidistant from the segment's endpoints.
The ratio of a circle's circumference to its diameter, approximately 3.14159. It is an irrational and transcendental number.
A closed plane figure formed by three or more straight line segments (sides) that meet at vertices.
A statement accepted as true without proof, serving as a starting point for logical reasoning and further theorems.
The distance from the center of a circle to any point on the circle, or a segment representing that distance.
A line that intersects a circle at exactly two points. A chord is the segment of a secant that lies inside the circle.
Figures that have the same shape but not necessarily the same size; corresponding angles are equal and corresponding sides are proportional.
A line that touches a circle at exactly one point (the point of tangency) and is perpendicular to the radius at that point.
A mathematical statement that has been proven true through logical deduction from axioms, definitions, and previously established theorems.
A line that intersects two or more other lines at distinct points, creating angle pairs such as alternate interior, alternate exterior, and corresponding angles.