母語、母語或母/父/母語言(也稱為動脈語言或L1)，是一個人從出生時或在關鍵時期接觸到的語言。在一些國家，母語指的是一個民族的語言，而不是自己的母語。說一種以上語言長大的孩子可以有一種以上的母語，并且會說兩種或多種語言。相比之下，第二語言是指除了母語之外的任何一種語言。

A first language, native language or mother/father/parent tongue (also known as arterial language or L1), is a language that a person has been exposed to from birth[1] or within the critical period. In some countries, the term native language or mother tongue refers to the language of one's ethnic group rather than one's first language.[2] Children brought up speaking more than one language can have more than one native language, and be bilingual or multilingual. By contrast, a second language is any language that one speaks other than one's first language.