The term ISIS is an acronym for the Islamic State of Iraq and Syria, a transnational Salafi jihadist militant organisation and an internationally unrecognised quasi-state. It is also widely known as ISIL (Islamic State of Iraq and the Levant) or by its Arabic acronym, Daesh. The organization's goal is to establish a worldwide caliphate and claim religious and political authority over all Muslims.
The group's origins trace back to 1999 with Abu Mus'ab al-Zarqawi's group, Jama'at al-Tawhid wal-Jihad. It later affiliated with al-Qaeda in Iraq (AQI) in 2004. The group changed its name to the Islamic State of Iraq and the Levant (ISIL) on April 8, 2013, and then proclaimed itself the Islamic State on June 29, 2014, upon declaring a caliphate. This declaration was a mechanism to establish a Sunni Islamic state led by a caliph, who they claimed was a successor to Muhammad.
The organization works by occupying significant territory, primarily in Iraq and Syria, and is notorious for its brutality. It has sought to galvanize local resources for its state-building project, shifting its focus from the "far enemy" (the US) to the "near enemy" (the Shia-dominated government in Baghdad). ISIS is designated as a terrorist organisation by the United Nations.
The group has undergone significant changes since its peak territorial control; it lost all of its territory in Syria by March 23, 2019, and its leader, Abu Bakr al-Baghdadi, was killed on October 27, 2019. While the group itself shortened its name to the Islamic State in 2014, the acronyms ISIS and ISIL remain entrenched in the international lexicon.