I really dont understand all the rim sizings etc. (I know its probably simple, but I just dont get it)

Im looking at a set of rims that have the size marked as 17x7.0. As I understand, this should fit a wrx just fine, but how does it compare to the size of the standard my02 wrx rim? Is it 17x7.5 or 17x7.0?
(I assume 17" refers to diameter and 7.0 refers to the width?)