I think what you may be referring to is more distinction between the American, meaning west coast style vs the rest of America. A West coast IPA is usually more hoppy and has more alcohol most of the time but not always.
Do you mean an American Pale Ale vs. an IPA? Either way I believe the real difference is amount of hops used. IPA or India Pale Ale was hopped up to keep the beer from spoiling on the long voyage to India from England. APA doesn't have that issue to worry about.
IMO American IPA includes American Hops: Cascade, Centennial, etc. and more hop aroma than your typical English IPA. They might also be a bit bigger than the English variety, but not by much.
There are also 'hybrid' IPA's, though the BJCP doesn't recognize them as being separate from American or British IPA's. These are beers with a combination of british and american ingredients, or 'imperial' style english IPA's.