Definition:Pyramid

Definition
Let $P$ be a polygon.

Let $Q$ be a point not in the plane of $P$.

From each vertex of $P$, let lines be drawn to $Q$.

The polyhedron which is contained by $P$ and the triangles formed by the sides of $P$ and the lines to $Q$ is a pyramid.

Linguistic Note
The word pyramid comes directly from the Classical Greek pyramis (πυραμίς) whose derivation is unknown.

In natural language the word usually refers to a square pyramid, and usually calls to mind the Great Pyramid of Giza.