\begin{definition}[Definition:Isotropic Quadratic Form]
Let $\mathbb K$ be a field of characteristic $\operatorname{char}\mathbb K \neq 2$.
Let $V$ be a vector space over $\mathbb K$.
Let $q : V\times V \mapsto \mathbb K$ be a quadratic form.
Then $q$ is '''isotropic''' {{Iff}} it represents $0$.
That is: $q(v) = 0$ for some $v\in V\setminus\{0\}$.
\end{definition}