The abbreviations that stand for the terrorist group is based on location. ISIS stands for Islamic State of Syria. Syria is known for having many terrorists in it. Another terrorist group is called the Daesh. They are different in that they follow the Sunni Islam. ISIL stands for Islamic State of Iraq and the Levant. The Levant is a location referring to the eastern area located along the Mediterranean Sea. All of these no matter what they are called are terrorist groups. They go to countries and hurt and kill people.
They do this because of their hate for many people. Many countries are trying to fight terrorist groups by bombing the area where they live in Syria, Iraq and other areas in the Middle East.