A first language (also mother tongue, native language, arterial language, or L1) is the language a person first learns. A person's first language helps them understand words and concepts in the style of that first language.
Sometimes first language means the language a person speaks best (his second language is the language he speaks less well than his first language, etc.). In this case first language, second language and third language show how well one speaks a language, so a person can have more than one first language or second language.
A lesson at Kituwah Academy on the Qualla Boundary in North Carolina. The language immersion school, operated by the Eastern Band of Cherokee Indians, teaches the same curriculum as other American primary schools, but Cherokee is the medium of instruction from preschool onward, and students learn it as a first language. Such schools have proven instrumental in the preservation and perpetuation of Cherokee.
First language for Kids. Kiddle Encyclopedia.