Googling this has only given me fairly detailed scientific papers and wikipedia (unusually) doesn't come up. Does anybody have a cheap and cheerful definition? Deducing these terms literally is not risk-free, but I suppose it involves a Gaussian probability distribution N(mu,sigma) where mu and sigma (may be one, may be both) do not vary linearly with a certain parameter .. potentially, time. Still, that leaves it too general ... I expect it may implicitly refer to some methods. Certainly, image filtering seems to be one of its more salient applications. However, I have to admit that I'm not very happy with usage of the term "non-linear". For me it has always meant "not specifically linear", which only implies to me a more general case. Anyhow, any clues welcome, thank you.