I'm currently reading through a journal online and I came across this particular mathematical equation:
$\Vert{a} - Tb - k \Vert_2 \leq \beta$
$a = [x,y]'$, T = $\begin{bmatrix}f & h\\e & z\end{bmatrix}$, b = [x,y]' and k = [g,h]
Basically, $a$ and $b$ are coordinates, T is a matrix of numbers and k is the difference in x,y coordinates of $a$ and $b$.
Particularly, I do not understand what does the $\Vert \Vert_2$ means. Could anyone please explain?
$\Vert \cdot \Vert_2$ denotes the euclidean norm,
https://en.wikipedia.org/wiki/Norm_(mathematics)