The most common acronym you hear is ISIS. But the Obama Administration calls it ISIL. A number of major news organizations — including the New York Times, the Washington Post, USA Today, The Guardian, and the Associated Press — call it the Islamic State. And a lot of Arabic-speaking people in the Middle East call it Daesh, sometime spelled DAIISH or Da'esh. As it turns out, it's not actually that confusing. There are perfectly good reasons for picking each of these names for the group. Here's a brief rundown of what each of the names means, and why different groups or media outlets might choose to use each one.
ISIS has gone by quite a few names over the years. It was founded in 1999 as Jamaat al-Tawhid wa-l-Jihad. That changed in 2004, when the group's founder, Abu Musab al-Zarqawi, pledged an oath to al-Qaeda. Then they were called Tanzim Qaidat al-Jihad fi Bilad al-Rafidayn — or, in English, al-Qaeda in Iraq.
After AQI took over huge swaths of in Iraq in 2006, the organization made a big step towards becoming ISIS: it declared itself a state in northern Iraq, and started calling itself the Islamic State in Iraq. In transliterated Arabic, that's al-Dawlat al-Iraq al-Islamiyah.
Pay attention now, because here's where the group becomes ISIS. By 2013, the group had taken a lot of territory in Syria and wasn't content with just calling itself the Islamic State in Iraq. On April 8 of that year, it began calling itself the Islamic State in Iraq and al-Sham — ISIS. Al-Sham is a difficult-to-translate Arabic term referring to a specific geographic area which includes Syria.
