Polygon
Closed figure made up of line segments

http://www.mathleague.com/help/geometry/polygons.htm#polygon

http://www.mathsisfun.com/geometry/polygons.html

http://www.math.com/school/subject3/lessons/S3U2L1GL.html

http://library.thinkquest.org/J002441F/polygons.htm

http://www.mathsisfun.com/geometry/regular-polygons.html