First language

First language
Appendix 2 of the Main Version of the Guide for the development of Language Education Policies in Europe. 2007. Council of Europe.
Definition
Language variety(ies) acquired in early childhood (approximately before the age of two or three years) in which the human language faculty was first acquired. This term is preferred to mother tongue, which is often inaccurate as the first language is not necessarily that of the mother alone.