Backspacing is more useful/helpful for Jeep & other 4x4 vehicle wheels, Offset is more useful/helpful for cars and sports cars. Too bad they get confused & used interchangeably because as said above, the terms are not interchangeable.
__________________ When you have a choice, buy American.
I wish everyone used backspacing to measure wheels. Looking at wheels for Subaru's is ridiculous. And it's all in METRIC!
If you are really having trouble try this site. It is awesome for figuring out car wheels! It's a lot easier to understand them if that's what you started with like me! 4x4 wheels are ridiculously easy in comparison...