\begin{definition}[Definition:Cylinder]
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A '''cylinder''' is a solid made by rotating a rectangle along one of its sides.
{{EuclidSaid}}
:''{{Definition:Euclid's Definitions - Book XI/21 - Cylinder}}''
{{EuclidDefRef|XI|21|Cylinder}}
In the above diagram, the rectangle $ADHG$ has been rotated around the side $GH$ to produce the '''cylinder''' $ACBEFD$.
\end{definition}