What does offest mean?

[kylryn]

I'm thinking about upgradeing to some different wheels and I'm not too sure what the offset means? it doesnt sound like its a clean fit. Can someone please explain this so the average joe understands? Thank you. 19x10: Offset: +79mm Backspace: 8 5/8 inch 18x9.5: Offset: +50mm Backspace: 7 1/4 inch 5x4.75: 18x9.5: Offset: +40mm Backspace: 6 7/8 inch 19x10: Offset: +56mm Backspace: 8 5/8 inch

[Mr turbo rotary]

http://www.needforspeed.co.uk/htmlpages/TechWheels.htm

[Glennm27]