Polygon

A polygon is a union of disjoint line segments that is path-connected.

Types, by number of sides.

1. There is no such mathematical entity as a one sided polygon in a plane. (For three dimensional analogies, see Mobius strip and Klein bottle.)
2. As with the one-sided polygon, there is no such thing as a two-sided polygon. (This would be two overlapping line segments.)
3. Triangle - see isosceles triangle, equilateral triangle, right triangle
4. Quadrilateral - See also square, rectangle, rhombus, and trapezoid
5. Pentagon
6. Hexagon - the shape of a bee hive cell, also used in some board games
7. Heptagon - not commonly encountered in everyday life
8. Octagon - used for stop signs in the U.S.