A polygon is a geometric figure in two dimensions with three or more sides. The name comes from two Greek words, poly, meaning "many,"
and gon, meaning "angle." A polygon always has as many angles as it has sides. And in general, polygons are named to indicate the number of sides or angles they contain. Thus, a hexagon has six ( hexa- means "six") sides and six angles.
Side: Any one of the straight lines that make up the polygon.
Vertex: A point where any two of the sides of a polygon meet to form an angle.
Angle: A figure formed by the intersection of two sides.
Diagonal: A line that joins any two nonadjacent (not next to each other) vertices.
Perimeter: The sum of the length of all sides.
Area: The space enclosed within the polygon.
Equilateral: A polygon in which all sides are equal in length.
Equiangular: A polygon in which all angles are the same size.
Regular: A polygon that is both equilateral and equiangular.
The most common kinds of polygons include:
Parallelogram: A quadrilateral (four-sided figure) in which both pairs of sides are parallel and equal.
Rhombus: A parallelogram in which all four sides are equal.
Rectangle: A parallelogram in which all angles are right angles.
Square: A rectangle in which all four sides are equal.