| Term | Definition |
| Perpendicular Lines | Two lines that intersect to form a right angle. |
| Parallel Lines | Two coplanar lines that do not intersect. |
| Conjecture | A statement that you think is true based on observations. |
| Theorem | A statement that you prove using logical reasoning. |
| Midpoint | A point that divides a segment into two congruent parts. |
| Segment Bisector | A line that passes through the midpoint of a segment. |
| Perpendicular Bisector | A line that bisects a segment and is also perpendicular to it. |
| Angle Bisector | A ray that divides an angle into two congruent parts. |
| Perpendicular Lines Theorem | If two coplanar lines are perpendicular to the same line, then they are parallel. |
| Distance from a Point to a Line | The shortest segment from a point to a line is the one that is perpendicular to the line. |
| Perpendicular Bisector Theorem | If a point is on the perpendicular bisector of a segment, then the point is equidistant from the endpoints of the segment. |
| Angle Bisector Theorem | If a point is on the bisector of an angle, then the point is equidistant from the sides of the angle. |