A lingua franca ( (listen); lit. 'Frankish tongue'; for plurals see § Usage notes), also known as a bridge language, common language, trade language, auxiliary language, vehicular language, or link language, is a language or dialect systematically used to make communication possible between groups of people who do not share a native language or dialect, particularly when it is a third language that is distinct from both of the speakers' native languages.

Lingua francas have developed around the world throughout human history, sometimes for commercial reasons (so-called "trade languages" facilitated trade), but also for cultural, religious, diplomatic and administrative convenience, and as a means of exchanging information between scientists and other scholars of different nationalities. The term is taken from the medieval Mediterranean Lingua Franca, an Italian-based pidgin language used especially by traders in the Mediterranean Basin from the 11th to the 19th centuries. A world language – a language spoken internationally and by many people – is a language that may function as a global lingua franca.