| A | B |
|---|
| Line Segment | A set of points on a line consisting of two endpoints and all the points between them. |
| Line | A straight one-dimensional figure having no thickness and extending infinitely in both directions. |
| Ray | Part of a line that starts at a particular point and extends infinitely far in one direction. |
| Polygon | A series of connected line segments that starts and ends at the same place and does not intersect itself anywhere in between. |
| Triangle | A three-sided polygon. |
| Quadrilateral | A four-sided polygon. |
| Pentagon | A five-sided polygon. |
| Hexagon | A six-sided polygon. |
| Heptagon | A seven-sided polygon. |
| Octagon | An eight-sided polygon. |
| Nonagon | A nine-sided polygon. |
| Decagon | A ten-sided polygon. |
| Vertex | A common endpoint of two sides of a polygon or an angle. |
| Diagonal | A segment that connects two nonadjacent vertices of a polygon. |
| Perimeter | The distance around a figure. |
| Angle | A figure formed by two line segments or rays with a common endpoint. |
| Axis of Symmetry | A line that divides a figure in half so that each half is the mirror image of the other. |
| Congruent | Two geometric objects having the same measure. |
| Right Angle | An angle that measures 90º. |
| Perpendicular Bisector | A line that intersects a given segment at right angles and divides it into two equal parts. |
| Regular Polygon | A polygon that has the most symmetry: all sides and angles are congruent. |
| Rhombus | An equilateral quadrilateral. |
| Parallelogram | A quadrilateral with opposite sides parallel. |
| Rectangle | An equiangular quadrilateral. |
| Square | An equiangular rhombus; an equilateral rectangle; or a regular quadrilateral. |
| Equiangular | A polygon with all angles congruent. |
| Equilateral | A polygon with all sides congruent. |
| Area | The number of square units that will fit in a given boundary. |
| Right Triangle | A triangle that has a right angle as one of its three angles. |
| Leg | One of the sides of a right triangle that is not the hypotenuse. |
| Hypotenuse | The longest side of a right triangle; the side opposite the right angle. |
| Altitude | A line segment drawn from one vertex to the opposite side that is perpendicular to that side. |
| Base | The side opposite the vertex in a triangle from which an altitude is drawn, if the altitude is within the triangle; also, either of the two parallel sides of a trapezoid. |
| Volume | The number of unit cubes needed to fill up a given space. |
| Similar | Two objects such that the distance between any two points of one object is a particular constant times the distance between the corresponding points of the other object. |
| Scaling Factor | The ratio of the lengths of corresponding sides of two similar figures. |
| Acute angle | An angle of measure less than 90º, but more than 0º. |
| Obtuse Angle | An angle of measure greater than 90º and less than 180º. |
| Reflex Angle | An angle of measure greater than 180º and less than 360º. |
| Straight Anlge | An angle of measure 180º. |
| Vertical Angles | Congruent angles that form opposite each other when two lines intersect. |
| Supplementary Angles | Two angles whose measures have a sum of 180 deg. |
| Parallel Lines | Straight lines in a plane that never intersect, no matter how far they are extended. |
| Transversal | A straight line that intersects two or more other coplanar straight lines at distinct points. |
| Corresponding Angles | Angles that are located in similar places along a transversal that intersects two lines; also, angles from congruent or similar figures in corresponding positions. |
| Alternate Interior Angles | Two nonadjacent angles on opposite sides of a transversal that are inside the lines crossed by the transversal. |
| Alternate Exterior Angles | Angles on opposite sides of a transversal and outside the lines crossed by the transversal. |
| Complementary Angles | Two angles whose measures have a sum of 90º. |
| Congruent Triangles (SSS,SAS,ASA,AAS) | Triangles that have the same shape and size |
| Isosceles Triangle | A triangle with two sides of equal length |
| Angle Bisector | A line or ray that divides an angle in half |
| Base Angles | The angles opposite the two equal sides in an isosceles triangles. A pair of angles that share a base as a common side in a trapezoid. |
| Convex Polygons | A polygon in which the measure of each angle is less than 180º. |
| Interior Angle | The angle that open toward the inside of the polygon |
| Exterior Angle | An angle formed by one side of a polygon and the extension of an adjacent side |
| Circle | The set of all points in a plane that are a fixed distance from a particular point. |
| Disk | A circle together with all the points inside it. |
| Circumference | The distance around a circle. |
| Diameter | A line segment that passes through the center of a circle and has both endpoints on a circle; also, the length of such segment. |
| Chord | A line segment with both its endpoints on the same circle. |
| Tangent Line | A straight line that touches a circle at only one point. |
| Collinear | Points on the same line. |
| Inscribed Polygons | A polygon with all its vertices on a circle. |
| Minor Arc | A portion of a circle that is smaller than a semicircle. |
| Major Arc | An arc that is larger than a semicircle. |
| Central Angle | An angle formed by two radii of a circle. |
| Sector of a circle | The region enclosed by two radii and the arc between them. |
| Segment of a circle | The region enclosed between an arc and a chord. |
| Inscribed Angles | An angle formed by two chords with an endpoint in common. |
