A triangle consists of three vertices. A triangle is composed of three lines, and the point where two line endpoints intersect is known as a vertex. A square has four vertices, whereas an octagon has eight vertices.

No matter how many lines are put into a polygonal shape, the number of vertices will always equal the number of sides.

A collinear vertex is a set of points on the same straight line.

Classification of triangles is based on the length of their sides and the inner angles of their corners.