Genus of $f(x,y,z) = x^2+y^2+7z^2$

Question

What does this statement mean?

The genus of $f(x,y,z) = x^2+y^2+7z^2$ consists of

$M_f = <1,1,7> $ and $M_2 = <1> \perp \begin{pmatrix} 2 & 1 \\ 1 & 4 \end{pmatrix}$.