Ebay What does: 1/8 Scale really mean?

On ebay I see alot of things that say 1/8 scale. Call me stupid or whatever you want, but just saying that for the size doesn't help me understand how big it is. How is it when it says that?? One eighth of an Inch?? Cause for somethings it says that but they obviously are bigger then that! so what does it mean?