Term Picture Definition Notation Classify by angle measure: Acute Angle An angle whose measure is less than 90° Two angles that share a common vertex and Adjacent angles side, but have no common interior points. A figure formed by two Angle rays with a common endpoint. Angle bisector A ray that divides an angle into two angles that are congruent When three points are Between collinear, then one point is between the other two. The set of all points in Circle a plane at a fixed distance from a fixed point. Collinear Points Points that lie on the same line Congruent Line segments that ̅̅ ̅̅̅ ̅̅ ̅̅̅ ̅ segments have the same length Complementary Two angles whose measures have the sum 90° Coplanar Points that lie in the same plane ( ) Distance along a J The length of a line JL=12 12 segment L Distance around The length of part of an arc the circumference of a ̂ circle Equal lengths Congruent segments have the same AB=TO measure. The set of points that ̅̅̅ ̅ two or more geometric Intersection figures have in common. ⋂ An undefined Line geometric term that has one dimension. It ⃡ extends without end in two directions. A portion of a line that consists of a defined Line Segment beginning and ̅̅̅ ̅ endpoint and all the points in between Two adjacent angles Linear Pair whose noncommon sides are opposite rays ̅̅̅ ̅ ̅̅̅ ̅ Midpoint A point that bisects a segment into two or congruent segments. Classify by angle measure: An angles whose Obtuse Angle measure is greater than 90° two rays with a ⃡ Opposite rays common endpoint that means “combined form a line with” A line that is a constant Parallel line distance from another ⃡ ⃡ line or plane Perpendicular A line that intersects a line, a line segment, lines/segments ̅̅̅ ̅̅ ̅̅̅̅ ̅ ray or plane to form a right angle An undefined term Point that has no dimensions. It is A usually represented by a dot ⃡ ̅̅̅ ̅ The point where two Point of Intersection lines or segments meet. ⋂ An undefined term Plane that has two dimensions. It extends without end in both dimensions Part of a line that consists of a point Ray called an endpoint and all points on the line that extend in one direction Classify by angle measure: Right angle An angle with measure equal to 90° A point, ray, line, ̅̅̅ ̅ so Segment bisector segment, or plane that that ̅̅̅ ̅ ̅ ̅̅ ̅ intersects a segment at its midpoint. ⋂ Classify by angle measure: An angle with measure Straight angle equal to 180° Supplementary Two angles whose angles measures have the sum 180° Vertical angles Two angle whose sides form two pairs of opposite rays .