Backspacing is the distance from the inside bolting surface of the wheel to the outer edge of the wheel from the inside point of view. Offset is the distance from the center of the wheel to the outer edges of the wheel...it plays a factor but not as much as bs. Offset is more for those import tuners looking for a flushed look.
With our jk, the most important is the backspacing. We have our rear links too close to the wheel as seen from my pic. If u go 5+ backspacing, ur not gonna need a lift but spacers to alleviate the problem. That's y the magic number is 4.5 or less, but I'm not saying 4.6 will not work....it's just a safety zone we have to play with.