\begin{definition}[Definition:Euclid's Definitions - Book XI/11 - Solid Angle]
{{EuclidSaid}}
:''A '''solid angle''' is the inclination constituted by more than two lines which meet one another and are not in the same surface, towards all the lines.<br/>Otherwise: A '''solid angle''' is that which is contained by more than two plane angles which are not in the same plane and are constructed to one point.''
{{EuclidDefRef|XI|11|Solid Angle}}
\end{definition}