Geometry Basics: Points, Lines, Angles, Triangles, and Polygons — Vocabulary

Vocabulary flashcards covering basic geometry terms from Points to Transversals.

Point

A location in space with no size.

Line

A straight path that goes on forever in both directions.

Ray

Part of a line that starts at one endpoint and extends forever in one direction.

Line Segment

Part of a line with two endpoints.

Plane

Flat surface that extends forever in all directions.

Acute Angle

An angle that measures less than 90 degrees.

Right Angle

An angle that measures exactly 90 degrees.

Obtuse Angle

An angle that measures more than 90 degrees but less than 180 degrees.

Straight Angle

An angle that measures exactly 180 degrees.

Adjacent Angles

Angles that share a side and a vertex but do not overlap.

Vertical Angles

Opposite angles formed by two intersecting lines that are always equal.

Complementary Angles

Two angles that add up to 90 degrees.

Supplementary Angles

Two angles that add up to 180 degrees.

Equilateral Triangle

A triangle with all sides equal and all angles equal.

Isosceles Triangle

A triangle with two sides equal and two angles equal.

Scalene Triangle

A triangle with all sides and all angles different.

Acute Triangle

A triangle in which all angles are less than 90 degrees.

Right Triangle

A triangle with one 90-degree angle.

Obtuse Triangle

A triangle with one angle greater than 90 degrees.

Polygon

A closed figure made up of straight line segments.

Concave Polygon

A polygon with at least one angle that caves in.

Convex Polygon

A polygon with all angles pointing outward; none cave in.

Midpoint

The exact middle of a line segment.

Bisector

A line or ray that cuts a segment or angle into two equal parts.

Parallel Lines

Lines that never cross and are always the same distance apart.

Perpendicular Lines

Lines that cross to form right angles.

Transversal

A line that cuts across two or more lines.