1) A language used as vernacular for communication amongst many speakers of different languages, i.e. a creole.
2) An early version of this, a mix of English, Spanish, Portuguese, Arabic and other languages with Italian.
3) (British) The English variant used by many Asian immigrants, mixing English with Indian tongues like Gujarati, Urdu/Hindi, Sinhalese, etc.
1) Swahili is the lingua franca in East Africa. Millions of people who speak indigenous languages also speak it for communication.
A commonly used language in a particular region.
English could be considered the lingua franca of the Internet, because it is on the majority of websites.
1337 5p34k has become the lingua franca of sorts of IRC and chat rooms.