| Term | Definition |
| Collinear | Three or more points contained in a line |
| Compass | A geometric tool that has two arms, one sharp and the another with a pencil that can be used to draw circles or arcs. |
| Straightedge | A geometric tool used to draw straight lines. |
| Degree | A unit of measurement of angles. |
| Congruent | In geometry, two figures are congruent if they have the same size and shape. |
| Perpendicular Lines | Lines that intersect and form right angles. |
| Angle Bisector | A line or segment that divides an angle into two equal parts. |
| Perpendicular Bisector | A line segment that is perpendicular to and passes through the midpoint of another line or segment. |
| vertex | A point where two or more segments or rays meet. |
| Arc | Part of any curve or part of the circumference of a circle. |
| Straight Angle | Is a line that measures 180 degrees. |
| Incenter of a Triangle | It is where the "angle bisectors" (lines that split each corner's angle in half) meet. |
| Noncollinear | Three or more points not contained in a line |
| Figure | A set of points in a plane. |
| Segment | The distance between two points (part of a line). |
| Circle | A A shape consisting of all points in a plane that are a given distance from a given point. |
| Circumcenter of a Triangle | A point where the "perpendicular bisectors" (lines that are at right angles to the midpoint of each side) meet. |
| Radius | A segment from the center of a circle to a point on the circle. |
| Equilateral Triangle | A triangle with all sides equal, and all angles equal (they are 60 degrees), |
| Midpoint | A point that is exactly between two endpoints on a segment. |
| Point of Concurrency | A point where three or more lines intersect in one place. |
| Geometric Construction | A set of instructions for drawing points, lines, circles, and figures in a plane. |
| Ray | Part of a line that has an endpoint (start point) but no end point. |
| Angle | The union of two noncollinear rays with the same endpoint. |
| Orthocenter of a Triangle | The point where the three "altitudes" of a triangle meet. An "altitude" is a line that goes through a vertex (corner point) and is at right angles to the opposite side. |
