\begin{definition}[Definition:Ordinary Space]
'''Ordinary space''' (or just '''space''') is a word used to mean '''the universe we live in'''.
The intuitive belief is that space is $3$-dimensional and therefore isomorphic to the real vector space $\R^3$.
Hence '''ordinary space''' is usually taken as an alternative term for Euclidean $3$-dimensional space.
\end{definition}