Definition:Cone/Base

Definition
Consider a cone consisting of the set of all straight lines joining the boundary of a plane figure $PQR$ to a point $A$ not in the same plane of $PQR$:


 * Cone.png

The plane figure $PQR$ is called the base of the cone.

Also see

 * Definition:Apex of Cone

Comment
Hence the colloquial phrase base over apex as the description of a particularly flamboyant physical tumble.