As int_19h notes, there are people (in the US) who believe that there is a difference between the meaning of the word "jail" and the meaning of the word "prison". And as int_19h also notes, those people are wrong; Americans will just be confused if you try to use the words differently. It's similar to the insistence of a group with near-perfect overlap that crimes for which jail time isn't a possible punishment can't be correctly referred to as "crimes".