1. Angles
1.1. Acute
1.1.1. Angle < 90 degrees
1.2. Obtuse
1.2.1. Angle > 90 degrees
1.3. Angles
1.3.1. The amount of turn between two straight lines that have a common end point (the vertex)
1.4. Right
1.4.1. Angle = 90 degrees
1.5. Straight
1.5.1. Angle = 180 degrees
2. Points
2.1. Midpoint
2.1.1. A point in the center of a segment
2.2. Point
2.2.1. A location in space
2.3. Endpoint
2.3.1. The point at the end of a ray or line segment
2.4. Vertex
2.4.1. Where two or more straight lines meet
3. Planes
3.1. Plane
3.1.1. A flat surface that is infinitely large and with zero thickness
3.2. Coplanar
3.2.1. A set of points, lines, line segments, rays, etc. that lie on the same plane
4. Lines
4.1. Line
4.1.1. The shortest distance between any two points on a plane
4.2. Segment
4.2.1. A part of a line that is bounded by two endpoints
4.3. Ray
4.3.1. A continuos line with a single endpoint
4.3.2. Opposite Rays
4.3.2.1. Two rays with a common endpoint
4.4. Bisector
4.4.1. The line that divides something into two equal parts
4.5. Collinear
4.5.1. When three or more points lie in a straight line
5. Lines and Planes
5.1. Congruent
5.1.1. Same shape and size
5.2. Conjecture
5.2.1. A statement thought to be true but not proven
5.3. Intersecting
5.3.1. Where lines or planes cross over (have a common point)
5.4. Perpendicular
5.4.1. Intersecting lines, or planes that form a right angle
5.5. Parallel
5.5.1. Always the same distance apart and never touching
5.6. Skew
5.6.1. Two nonparallel lines in space that do not intersect