\begin{definition}[Definition:Pyramid]
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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'''.
{{EuclidDefinition|book = XI|def = 12|name = Pyramid}}
\end{definition}