lingua franca

Any language that is used as a means of communication by groups who do not themselves normally speak that language; for example, English is a lingua franca used by Japanese doing business in Finland, or by Swedes in Saudi Arabia. The term comes from the mixture of French, Italian, Spanish, Greek, Turkish, and Arabic that was spoken around the Mediterranean from the time of the Crusades until the 18th century.

Many of the world's lingua francas are pidgin or trade languages; for example, Bazaar Hindi (Hindustani), Bazaar Malay, and Neo-Melanesian (also known as Tok Pisin), which became the official language of Papua New Guinea.