Azerbaijani or Azeri, also referred to as Azeri Turkic, is a Turkic language from the Oghuz sub-branch. It is spoken primarily by the Azerbaijani people, who live mainly in the Republic of Azerbaijan, where the North Azerbaijani variety is spoken, and in the Azerbaijan region of Iran, where the South Azerbaijani variety is spoken. North Azerbaijani has official status in the Republic of Azerbaijan and Dagestan, but South Azerbaijani does not have official status in Iran, where the majority of Azerbaijani people live. Azerbaijani is also spoken to lesser varying degrees in Azerbaijani communities of Georgia and Turkey and by diaspora communities, primarily in Europe and North America.

In linguistics, mutual intelligibility is a relationship between languages or dialects in which speakers of different but related varieties can readily understand each other without prior familiarity or special effort. It is sometimes used as an important criterion for distinguishing languages from dialects, although sociolinguistic factors are often also used.