point
An exact location in space usually shown by a dot.
ray
A straight path that extends infinitely from a point called its endpoint.
line
A straight path that extends infinitely in opposite directions.
line segment
A straight path joining two points. The two points are called the endpoints of the segment.
parallel lines
Two or more lines that never meet or cross and are always the same distance apart no matter how far they extend.
intersecting lines
Lines that meet or cross one another.
perpendicular lines
Lines that meet at right angles.
angle
A figure that is formed by two rays or two line segments with a common endpoint.
vertex
The point where the rays of an angle or the sides of a polygon meet.
right angle
An angle that measures 90 degrees.
acute angle
An angle that measures greater than 0 degrees and less than 90 degrees.
obtuse angle
An angle that measures greater than 90 degrees and less than 180 degrees.
straight angle
An angle that measures 180 degrees.
reflex angle
An angle that measures greater than 180 degrees and less than 360 degrees.
polygon
A closed, 2-dimensional figure that is made up of line segments joined end to end. The line segments of a polygon may not cross.
triangle
A polygon with three sides.
equilateral triangle
A triangle with all three sides equal in length. All three angles have the same measure.
right triangle
A triangle with a 90 degree angle.
quadrangle/quadrilateral
A polygon with 4 sides, 4 angles, and 4 vertices.
square
A quadrilateral with all sides equal and four right angles.
rhombus
A quadrilateral whose sides are all the same length.
rectangle
A quadrangle with four right angles and with opposite sides the same length.
parallelogram
A quadrilateral with two pairs of parallel sides. Squares, rectangles, and rhombuses are parallelograms, but trapezoids and kites are not.
trapezoid
A quadrilateral that has exactly one pair of parallel sides.
kite
A quadrilateral with two pairs of adjacent equal sides. The four sides cannot all have the same length. A rhombus is not a kite.
regular polygon
A polygon whose sides are all the same length and whose angles are all equal.
pentagon
A polygon with five sides.
hexagon
A polygon with six sides.
heptagon
A polygon with seven sides.
octagon
A polygon with eight sides.
nonagon
A polygon with nine sides.
decagon
A polygon with ten sides.