Vertex

B is an ear because the line between C and D is completely inside the shape. C is a mouth because the line between A and B is completely outside the shape.

A vertex is a corner. More than one vertex are called vertices. A vertex is a point where two or more lines, curves, rays, or sides meet, and is often represented by letters such as $P$, $Q$, $R$ and $S$.

For example, the vertex of an angle is the point where the two edges of the angle intersect, and a vertex of a cube is simply one of its corners—of which there are eight.

The concept of vertex applies to both two-dimensional and three-dimensional geometrical objects. For example, a tetrahedron has four vertices, and a pentagon has five vertices.

Related pages

• Graph (mathematics)
• Vertex figure