\begin{definition}[Definition:Orthogonal (Bilinear Form)/Radical]
Let $\mathbb K$ be a field.
Let $V$ be a vector space over $\mathbb K$.
Let $b : V\times V \to \mathbb K$ be a reflexive bilinear form on $V$.
The '''radical''' of $V$ is the orthogonal complement of $V$:
:$\operatorname{rad}(V) = V^\perp$
\end{definition}