Nullspace

Also called the Kernel. If $T$ is a linear transformation of $\Bbb{R}^n$, then Null($T$) is the set of all Vectors ${\bf X}$ such that $T({\bf X}) = {\bf0}$, i.e.,

$$\mathop{\rm Null}(T) \equiv \{{\bf X}: T({\bf X}) = {\bf0}\}.$$