"The Islamic State of Iraq and the Levant (ISIL), also known as the Islamic State of Iraq and al-Sham, the Islamic State of Iraq and Syria (ISIS), officially known as the Islamic State (IS) and by its Arabic language acronym Daesh, is a Salafi jihadist militant group and former unrecognised proto-state that follows a fundamentalist, Salafi doctrine of Sunni Islam."
Everyone in the rest of the world calls them Daesh. We're the only ones who call them anything else, unless another country is talking to us – in which case they call them ISIS because otherwise, we go, "Huh?"