多边形是平面的封闭图形、由有限线段（大于2）组成，且首尾连接起来划出的形状。

顶点

指三角形中任何两边相交所形成的交点或锥体的尖顶。

边

内角 

顶点相邻的两边所组成的角度。n边形的内角和为(n-2)×180°

外角 

对于某内角来说，其相应的外角角度为180°减去内角角度，多边形的所有外角之和恒等于360°。

对角线 

以不毗连顶点为端点的线段

In elementary geometry, a polygon /ˈpɒlɪɡɒn/ is a plane figure that is bounded by a finite chain of straight line segments closing in a loop to form a closed chain or circuit. These segments are called its edges or sides, and the points where two edges meet are the polygon's vertices (singular: vertex) or corners. The interior of the polygon is sometimes called its body. An n-gon is a polygon with n sides; for example, a triangle is a 3-gon. A polygon is a 2-dimensional example of the more general polytope in any number of dimensions.