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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 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 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°
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 triangle 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.