Lingua franca has 3 different meanings across 2 categories:
a common language used by speakers of different languages
"Koine is a dialect of ancient Greek that was the lingua franca of the empire of Alexander the Great and was widely spoken throughout the eastern Mediterranean area in Roman times"
A common language used by people of diverse backgrounds to communicate with one another, often a basic form of speech with simplified grammar, particularly, one not the first language of any of its speakers.
Sabir, the Italian-based pidgin that served as the lingua franca of Mediterranean trade in the late Middle Ages and early Modern period (c. 11th–19th centuries)