Azerbaijani or Azeri is Azerbaijan's national language. It actually belongs to the Turkic language family and has over 23 million native speakers. When the nation split between Iran and Russia in the 19th century, it evolved and became two forms, North and South Azerbaijani.
North Azerbaijani has official status in Azerbaijan. There, it's a widely spoken language. South Azerbaijani, meanwhile, isn't recognized as an official language in the nation. It's also not recognized as an official language in Iran despite most of the residents being Azerbaijani people. Regardless, it still has millions of speakers, including the Azerbaijani communities in Turkey and Georgia and diaspora communities in North America and Europe.