'Exclusion' layer + GIMP

Hi guys ♥

I just have one little question cause its been driving me nuts and I thought it was about time I actually asked :P

On 99% of icon tutorials, one of the first steps is to include an "Exclusion" layer. I use GIMP. Is there an exclusion layer option in Gimp, and if so where on earth is it?! :)
(And if not, what is the closest alternative?)

Thanks heaps ♥