What does y^2-x^2=16 represent?

I know it's a hyperbola, but I read that:

if B2 − 4AC > 0, the equation represents a hyperbola;

if we also have A + C = 0, the equation represents a rectangular hyperbola.

Here A+C=0, but is this actually rectangular??? I thought it would just be a normal hyperbola....aren't rectangulars of the form xy=k