What's the difference between imperial pale ale and indian pale ale? I've seen both refered to as IPA, which is the real IPA and how are they different?
Most often, if you see IPA, it's an "India pale ale".

"Imperial pale ale" is an informal, descriptive style (i.e., a strong pale ale), whereas "india pale ale" is a BJCP recognized style.  India pale ales are primarily understood as a hopped-up version of a pale ale, made to withstand long travels.  Beers with an "imperial" nomenclature (typically synonymous with "double") are brewed to be a stronger, higher ABV -- think double IPAs, imperial stouts, etc.