| an angle that measures less than 90o | Acute Angle |
| angles that share a common side | Adjacent Angles |
| interior angles of a transversal with the same measure | Alternate Interior Angles |
| exterior angles of a transversal with the same measure | Alternate Exterior Angles |
| formed when two rays have the same endpoint | Angle |
| the sum of adjacent angles equals 90o | Complementary Angles |
| angles with the same measure | Congruent Angles |
| Angles that are in the same position (matchers) on a transversal | Corresponding Angles |
| an angle that measures greater than 90o | Obtuse Angle |
| angles that are across from each other - usually congruent | Opposite Angles |
| a device that is used to measure an angle | Protractor |
| an angle that measures 90o | Right Angle |
| one of the rays that form an angle | Side |
| an angle measuring 180o | Straight Angle |
| the sum of adjacent angles equals 180o | Supplementary Angles |
| The point where two rays meet to form an angle | Vertex |
| angles that are opposite each other when lines intersect. (congruent) | Vertical Angles |
| use a compass to find the midpoint of a line Line Segment | Bisect |
| a device used to draw arcs and circles | Compass |
| points that are on the same line | Collinear |
| figures that are on the same plane |
Coplanar |
| Lines that cross at a vertex | Intersecting |
| a group of points that follow a never ending, straight path | Line |
| lines from the same plane that will never cross | Parallel |
| Intersecting lines that form a set of right angles. | Perpendicular |
| an endless flat surface that is named by any 3 points. | Plane |
| an exact location in space | Point |
| a part of a line with one end point | Ray |
| a part of a line with 2 end points | Line Segment |
| lines that are not on the same plane. | Skew |
| parallel lines that are crossed by an intersecting line | Transversal |
| a triangle with all angles less than 90o | Acute Triangle |
| two shapes of exactly the same size and proportions | Congruent |
| line segment that connects two nonadjacent vertices of a polygon | Diagonal |
| a triangle with all sides the same measure | Equilateral Triangle |
| a six sided polygon | Hexagon |
| a triangle with 2 sides the same measure | Isosceles Triangle |
| a triangle with one angle that is greater than 90o | Obtuse Triangle |
| an 8 sided polygon | Octagon |
| a quadrilateral with 2 pairs of parallel sides | Parallelogram |
| a five sided polygon | Pentagon |
| a closed plane figure made by three or more line segments | Polygon |
| a four sided polygon | Quadrilateral |
| a parallelogram with four 90o angles | Rectangle |
| a polygon in which all sides and angles are congruent | Regular Polygon |
| a parallelogram with 4 equal sides | Rhombus |
| a triangle with one angle that is 90o | Right Triangle |
| a triangle with no side having an equal measure | Scalene Triangle |
| a rectangle with 4 equal sides | Square |
| a quadrilateral with only 1 pair of parallel sides | Trapezoid |
| common endpoints that form a "corners" of a polygon | Vertices |
| the line a figure is "flipped" over | Line of Reflection |
| a line that divides a figure in such a way as to create 2 congruent or matching figures. | Line of Symmetry |
| move or change the position of a figure | Transformation |
| slide a figure | Translation |
| flip a figure (mirror image) | Reflection |
| turn a figure around a point. | Rotation |
| figures have the same shape - may not have the same size | Similar |
| a repeating arrangement of one or more shapes that completely covers a plane - no gaps or over laps | Tessellation |