bilinear

A bilinear function.

(of a function in two variables) Linear (preserving linear combinations) in each variable.

“The function f(x,y)=xy is bilinear, because f(ax+bu,y)=af(x,y)+bf(u,y) and f(x,ay+bv)=af(x,y)+bf(x,v) for all values.”

Of or pertaining to a Möbius transformation (type of conformal map representable as the ratio of two linear functions).

“bilinear isotropic hardening”