<P> In geometry, a pyramid is a polyhedron formed by connecting a polygonal base and a point, called the apex . Each base edge and apex form a triangle, called a lateral face . It is a conic solid with polygonal base . A pyramid with an n - sided base has n + 1 vertices, n + 1 faces, and 2n edges . All pyramids are self - dual . </P> <P> A right pyramid has its apex directly above the centroid of its base . Nonright pyramids are called oblique pyramids . A regular pyramid has a regular polygon base and is usually implied to be a right pyramid . </P> <P> When unspecified, a pyramid is usually assumed to be a regular square pyramid, like the physical pyramid structures . A triangle - based pyramid is more often called a tetrahedron . </P> <P> Among oblique pyramids, like acute and obtuse triangles, a pyramid can be called acute if its apex is above the interior of the base and obtuse if its apex is above the exterior of the base . A right - angled pyramid has its apex above an edge or vertex of the base . In a tetrahedron these qualifiers change based on which face is considered the base . </P>

What do you call a pyramid with a triangular base