Miketrd, I copy/pasted from a tire shop:
The offset of a wheel is the distance from the mounting surface of the wheel to the true centerline of the rim. A positive offset means the mounting surface of the wheel is positioned in front of the true centerline of the rim / tire assembly. This in effect brings the tire in to the fender well more. Conversely, a negative offset means the mounting surface of the wheel is behind the true centerline of the rim / tire assembly. This will cause the tire to stick out away from the vehicle.
Rule of thumb: The smaller the #, the more it sticks out, the higher the # the more it goes in.
So if our stock offset is +38mm, you don't really want to increase the offset too much, otherwise (say for example +45mm) it will sit into the fender way too much...from the side it will look like it tucks into the car (sorta like when you put on steelies for the winter).
Whereas, something +38mm & lower, it will stick out more closer to the fenders...so they will look more flush with the body.
Hope you understand what I'm saying.