Download Geometry Definitions * Unit 2

Geometry Definitions – Unit 1
1. Point (undefined) – has location only. No length, no width, no depth. Named using a capital letter or a
coordinate pair.
2. Line (undefined) – Lines extend indefinitely and have no thickness or width. Named using a single
lowercase letter or by any two points on the line.
3. Plane (undefined) – A flat surface that extends in all directions containing at least 3 [non-collinear]
points. Named using a single lowercase letter or by 3 [non-collinear] points.
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collinear points – points that lie on the same line.
coplanar points – points that lie in the same plane.
coplanar lines – lines that lie in the same plane.
non-collinear points – points that do NOT lie on the same line.
non-coplanar points – points that do NOT lie in the same plane.
non-coplanar lines – lines that do NOT lie in the same plane.
10. segment (line segment) – part of a line that consists of two endpoints and all points between them.
Segments are named by their endpoints.
11. Parallel lines – lines in the same plane that do not intersect.
12. Parallel planes – Planes that do not intersect.
13. Skew lines – lines that do not intersect and are not in the same plane.
14. Congruent – having the same size and shape.
15. Congruent segments – segments that have the same length.
16. Midpoint – a point M is the midpoint of segment PQ if M is between P and Q, and PM = MQ.
17. Segment bisector – a segment, line, or plane that intersects a segment at its midpoint.
18. Ray – a part of a line that has an endpoint and contains all the points of the line without end in one
direction. (A one-directional line.)
19. Angle – a figure consisting of two non-collinear rays with a common endpoint. [Show “vertex” on the
drawing.]
20. Congruent angles – angles that have the same measure.
21. Right angle – an angle whose measure is 90 degrees.
22. Perpendicular lines – two lines that intersect to form a right angle.
23. Acute angle – an angle whose measure is between 0 and 90 degrees.
24. Obtuse angle – an angle whose measure is between 90 and 180 degrees.
25. Straight angle – an angle whose measure is 180 degrees.
26. Angle bisector – a ray that separates an angle into two equal angles.
27. Vertical angles – Two non-adjacent angles formed by two intersecting lines.
28. Complementary angles – 2 angles whose measures have a sum of 90 degrees.
29. Supplementary angles – 2 angles whose measures have a sum of 180 degrees.
30. Linear pair – 2 angles that are adjacent and supplementary.