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Geometry terms and definitions

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


A location in space - a dot on a piece of paper


Connects two points via the shortest path and continues indefinitely (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 segments 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°


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 triangle with all three sides of equal length (each internal angles = 60°)


Distance (line segment) from center of a circle to any point on that circle's circumference.


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)


Distance around a circle (the perimeter)


A line segment joining two points on a curve.


Part of a curve

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

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