are they the same thing or are they different??
i bought some 18's with 5.5" backspacing and they stick out wider than i like so when i get my 37's im going to get some 20's... what offset and/or backspacing do you think looks the best on a truck with 8" lift?

 

offset is how far in or out the actual face of the wheel is, were as backspacing is how far the whole wheel will be in or out, most of the wheel for our truck have around a -9ish offset but back is different from wheel to wheel. Just remember you can always install fender flares to compensate for tires sticking out too far

 

They are different, however they are directly proportional. The more positive your offset the more backspacing you'll have resultig in your wheel sitting deeper in your fender well and vice versa. The BS and OS are determined by the relation of the center bore to the centerline. Here's a pic to help you understand http://filmat11inc.com/images/wheel%20diagram.gif

 

Keep in mind some lift kits require a certain amount of backspacing.

 

To answer your question arance, mine are 4 1/2" backspacing with a -12mm offset.