A pyramid is named by the shape of its ‘base’. A pyramid with a triangular base is a triangle-based pyramid. A tetrahedron is a triangular pyramid with all equilateral triangle faces.

The green equilateral triangle extending from the Vitruvian Man's crotch down ... If four spheres are connected as closely as possible into a pyramid shape, for instance, then the height to base ratio ...

The states with the equilateral triangle shape also have a dual description in terms of particle-hole excitations in a mean-field picture.