Patois is basically any bastardised version of an existing language. In Haiti the patois (creole) is a local dialect of French mixed with other words (African languages, Spanish, native etc). In Jamaica the patois is exactly the same with English.
I suppose they are different languages in a sense, but haven't evolved over the same time period of their base languages. It's similar to the Scots language (not to be confused with Scottish Gaelic), a very strong localised dialect. I grew up listening to Jamaican patois all the time and it's very easy to understand for an English speaker with a bit of familiarity, the same as the other English-speaking Caribbean islands, but I couldn't understand variations from Spanish or French speaking islands.