Azerbaijani (/ˌæzəbaɪˈdʒɑːni, ˌɑː-, -ˈʒɑːni/) or Azeri (/æˈzɛəri, ɑː-, ə-/), sometimes also Azeri Turkic or Azeri Turkish, is a term referring to two Turkic lects (North Azerbaijani and South Azerbaijani) that are spoken primarily by the Azerbaijanis, who live mainly in the Republic of Azerbaijan and Iran. North Azerbaijani and South Azerbaijani have significant differences in phonology, lexicon, morphology, syntax, and sources of loanwords.
North Azerbaijani has official status in the Republic of Azerbaijan and Dagestan (a federal subject of Russia) but South Azerbaijani does not have official status in Iran, where the majority of Azerbaijanis live. It is also spoken to lesser varying degrees in Azerbaijani communities of Georgia and Turkey and by diaspora communities, primarily in Europe and North America.
Both Azerbaijani lects are members of the Oghuz branch of the Turkic languages. The standardized form of North Azerbaijani (spoken in the Republic of Azerbaijan and Russia) is based on the Shirvani dialect, while Iranian Azerbaijani uses the Tabrizi dialect as its prestige variety. Azerbaijani is closely related to Gagauz, Qashqai, Crimean Tatar, Turkish and Turkmen, sharing varying degrees of mutual intelligibility with each of those languages. According to linguistic comparative studies, the closest relative of Azerbaijani is the Turkmen language.
(Courtesy of Azeri Language Wikipedia)