"A pyramid (from Greek: πυραμίς pyramis)[1][2] is a structure whose outer surfaces are triangular and converge to a single point at the top, making the shape roughly a pyramid in the geometric sense. The base of a pyramid can be trilateral, quadrilateral, or any polygon shape"

https://en.wikipedia.org/wiki/Pyramid_(geometry):

"In geometry, a pyramid is a polyhedron formed by connecting a polygonal base and a point, called the apex. [...] When unspecified, a pyramid is _usually_ assumed to be a regular square pyramid"

Note the _usually_.

If you shrink a side elevation of the Shard to 10% of its actual height, it looks like an eight-storey tall pyramid: http://imgur.com/a/Vslkl