second language

noun

1. a language learned by a person after his or her native language, especially as a resident of an area where it is in general use.
2. a language widely used, especially in educational and governmental functions in a region where all or most of its speakers are nonnative, as English in India or Nigeria.

noun

1. a language other than the mother tongue that a person or community uses for public communication, esp in trade, higher education, and administration
2. a non-native language officially recognized and adopted in a multilingual country as a means of public communication