Which of the following describes the form of a pyramid?
three triangular sides and square base
four squares and a triangular base
four triangular sides and a square base

Most pyramids consist of four triangular sides and a square base. The pyramid is a polyhedron for which the base is a polygon and all lateral faces are triangles. A pyramid is typically described by the shape of its base. For instance, a triangular pyramid has a base that is a triangle, and a hexagonal pyramid has a base that is a hexagon.