母语，或第一语言，有三种解释。一者为：一个人出生以后，最早接触、学习、并掌握的一种或几种语言。母语一般是自幼即开始接触、并持续运用到青少年或之后；并且，一个人所受的家庭或正式教育中，尤其是早期，有相当部分是通过母语传授的；母语另一个解释则是一个人的民族语，并不一定是一个人最早接触、学习、并掌握的「语言」，例如「母岛」、「母国」等，仅仅表示「根源」的意思，母语不仅仅表示为母亲对某个人说的语言，而是他认定的民族语。为了避免对多母语者的母语定义产生歧义，产生出的第三种解释为不借用其他语言进行（如翻译等方式）学习而学会的语言。（如婴幼儿看图片学习名词即为母语学习）

A first language (also native language, mother tongue, arterial language, or L1) is the language or are the languages a person has learned from birth or within the critical period, or that a person speaks the best and so is often the basis for sociolinguistic identity . In some countries, the terms native language or mother tongue refer to the language of one's ethnic group rather than one's first language. Children brought up speaking more than one language can have more than one native language, and be bilingual.