Geometry terms and definitions

To save you having to refer to a dictionary, we’ve listed below some of the more common geometry terms and geometry definitions below to help you help with your child’s geometry homework.

Term	Definition/ Description
Point	A location in space - a dot on a piece of paper
Line	Connects two points via the shortest path and continues indefintely (forever) in both directions
Line Segment	Part of a line between two points
Perpendicular Line Segment	Line Segments that intersect (cross) at an angle of 90°
Parallel Line Segments	Line segements that never intersect (they are always the same distance apart)
Right Angle	An angle that measures 90°
Acute Angle	An angle that measures less than 90°
Obtuse Angle	An angle that measures more than 90°
Vertex	Point at which two line segments intersect (forming an angle)
Scalene Triangle	A triangle with all three sides with different lengths
Isosceles Triangle	A triangle with two equal length sides (and two equal internal angles)
Equilateral Triangle	A traingle with all three sides of equal length (each internal angles = 60°)
Radius	Distance (line segment) from center of a circle to any point on that circle's circumference.
Diameter	A line segment (or length) joining two points on a circles circumference and passes through the circle's center (twice the length of the radius)
Circumference	Distance around a circle (the perimeter)
Chord	A line segment joining two points on a curve.
Arc	Part of a curve

This Math Open Reference Project provides additional information with more geometry terms and definitions.