What is a lingua franca?

A lingua franca (free language) is a language that is adopted as a common means of communication between speakers whose native languages are different. It is often used in trade, diplomacy, and multicultural regions where people need to communicate but do not share a first language. Examples of historical and modern lingua francas include Latin in the Roman Empire, Mandarin in Chinese civilization, French in European diplomacy, and English in international business and aviation today.