# Is there a name of the rule that $\lVert x + z \rVert^2 + \lVert x - z \rVert^2 = 2 \lVert x \rVert^2 + 2\lVert z \rVert^2$?

I'm a bit new to real analysis. Today, I came across this particular equality, whcih seems obvious to me. $$\lVert x + z \rVert^2 + \lVert x - z \rVert^2 = 2 \lVert x \rVert^2 + 2\lVert z \rVert^2$$ Is there a specific name for this?