\begin{definition}[Definition:Orthogonal Subspaces]
Let $\struct {V, \innerprod \cdot \cdot}$ be an inner product space.
Let $A$ and $B$ be closed linear subspaces of $V$.
Let $A$ and $B$ be orthogonal in $V$.
Then we say that $A$ and $B$ are '''orthogonal subspaces'''.
\end{definition}