# Two Words to Describe a Polygon

Although there are many types of polygons, if you had to describe a polygon in just two words, you might say it is a "plane figure." Because a plane is a flat, two-dimensional space, a polygon has width and height, but no depth. It is composed of straight lines and is a closed figure.

##### Regular or Irregular

A polygon with equal angles and equal sides is called a regular polygon. Any other polygon shape is called irregular.

##### Concave or Convex

If a polygon has no inward-pointing angle of more than 180 degrees, its shape is convex. Polygons with internal angles greater than 180 degree are called concave, because they appear to be crumbling inward or caving inward..

##### Simple or Complex

Simple polygon have just one boundary; in other words, none of the lines cross each other. By contrast, complex polygons have lines that intersect each other in at least one area.

##### Examples

Polygons are named by their number of sides. Examples include triangles, which have three connected line segments; quadrilaterals, which have four connected line segments; pentagons, which have five connected line segments; and hexagons, which have six connected line segments. Each of these may or may not have line segments of equal length.

##### Photo Credits

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