This document defines and describes basic geometry terms including points, lines, line segments, rays, planes, angles, and the relationships between lines such as intersecting, parallel, and perpendicular lines. Points mark exact locations, lines have no endpoints, line segments connect two endpoints, rays have one endpoint and extend in one direction, planes are flat endless surfaces, and angles are formed by two rays with a shared endpoint which can be acute, obtuse, right, or straight.

1. Chapter 23 Lesson 1 Geometry

2. Point A point marks an exact location in space. Use a letter to name a point.

3. Line A line is an endless straight path. It has no endpoints. Use two points on the line to name the line.

4. Line Segment A line segment is part of a line between two endpoints. Use the two endpoints to name the line segment.

5. Ray A ray is part of a line that has one endpoint and goes on forever in one direction. Use an endpoint and one other point on the ray to name a ray.

6. Plane A plane is an endless flat surface. Use three points that are not on a line to name the plane

7. Angle An angle is formed by two rays with the same endpoint. An angle can be named by three letters – a point from each side and the vertex as the middle letter. It can also be named by a single letter, its vertex.

8. Right Angle A right angle measures 90°

9. Acute Angle An acute angle is greater than 0 and less than 90°

10. Obtuse Angle An obtuse angle is greater than 90 and less than 180°

11. Straight Angle A straight angle measures 180°

12. Intersecting Lines Intersecting lines are lines that cross at one point.

13. Parallel Lines Parallel lines are lines in a plane that never intersect and are the same distance apart at every point.

14. Perpendicular Lines Perpendicular lines are lines that intersect to form four right angles.