I'm looking at getting wheels for the old truck and came across these:

vision style 256
anyways, i was looking at the 17 x 11 for the rear. Can someone explain the difference (or what it means) between offsett and backside?
The webpage says:
17 x 11 -19mm offset 5.25" backside
I've heard of backspacing, is backside the same thing?
Does anyone know if these will fit our trucks?