Multilingualism is the use of more than one language, either by an individual speaker or by a group of speakers. When the languages are just two, it is usually called Bilingualism. It is believed that multilingual speakers outnumber monolingual speakers in the world's population. More than half of all Europeans claim to speak at least one language other than their mother tongue; but many read and write in one language. Being multilingual is advantageous for people wanting to participate in trade, globalization and cultural openness.
https://en.wikipedia.org/wiki/Multilingualism