Basic Geometry Definitions

Collinear

two or more points that lie on the same line

line segment

a subset of a line consisting of two endpoints, and all and points between them

midpoint of a segment

a point on a line segment that divides it into two equal lengths

segment bisector

a line that intersects a line segment at its midpoint

ray

a subset of a line consisting of one endpoint and all points to one side

opposite rays

two rays with a common endpoint that point in opposite directions to form a line

angle

two rays with a common endpoint

vertex

the common endpoint of two rays

interior of an angle

all points lying between two rays in an angle

adjacent angles

two angles sharing a common vertex and a common ray between them

linear pair

adjacent angles whose non-common rays form opposite rays

vertical angles

a pair of non-adjacent angles formed by the intersection of two lines

angle bisector

a line that divides an angle into two angles of equal measure

acute angle

an angle whose measure is greater than 0° and less than 90°

obtuse angle

an angle whose measure is greater than 90° and less than 180°

right angle

an angle whose measure is 90°

reflex angle

an angle whose measure is greater than 180°

straight angle

an angle whose measure is 180°

complementary angles

two angles whose measures sum to 90°

supplementary angles

two angles whose measures sum to 180°

perpendicular lines

two lines that intersect to form angles that measure 90°

perpendicular bisector

a line that intersects a line segment at its midpoint and is perpendicular to the line segment

congruent

two objects with equal lengths and/or equal angle measures