A square is a polygon with four vertices. The shape has four equal sides and four 90-degree angles; thus, it is called a regular quadrilateral. The sides meet in four corners, which are called vertices.
A vertex is defined in geometry as the common endpoint of two or more rays or line segments. In a more simplified meaning, it is a point where lines meet. This term is generally used to refer to the corners of a polygon or polyhedron formed by the intersection of the edges or faces. Two lines that are joined at a vertex form an angle. In a square, the included angle at each vertex is referred to as an interior angle of the quadrilateral.