A pyramid is a structure
Nonbuilding structure
Nonbuilding structures, also referred to simply as structures, are those not designed for continuous human occupancy. The term is used by architects and structural engineers to distinctly identify structures that are not buildings....

 whose outer surfaces are triangular and converge at a single point. The base of a pyramid can be trilateral, quadrilateral, or any polygon shape, meaning that a pyramid has at least three triangular surfaces (at least four faces
Face (geometry)
In geometry, a face of a polyhedron is any of the polygons that make up its boundaries. For example, any of the squares that bound a cube is a face of the cube...

 including the base). The square pyramid
Square pyramid
In geometry, a square pyramid is a pyramid having a square base. If the apex is perpendicularly above the center of the square, it will have C4v symmetry.- Johnson solid :...

, with square base and four triangular outer surfaces, is a common version.

A pyramid's design, with the majority of the weight closer to the ground, and with the pyramidion
A pyramidion is the uppermost piece or capstone of an Egyptian pyramid in archaeological parlance. They were called benbenet in the Ancient Egyptian language, which associated the pyramid as a whole with the sacred benben stone...

 on top means that less material higher up on the pyramid will be pushing down from above.