Isis is an Egyptian goddess who presides over the act of embalming the dead and is wife to Osiris who--oh wait, you mean ISIS. ISIS was the fictional headquarters of a team of secret agents on the TV show, Archer, before having to change its name because of...oh. That ISIS.
They're a terrorist organization. Ho-hum. They pulled off a few successful attacks and everyone's losing their minds--because, you know, the best way to react to terrorists, who seek to fill their enemies with fear, is to become delirious with fear, right?
Anyway, they're comprised of a small number of really, really extremist Muslims who think the vast majority of Muslims who DON'T blow up every building in sight are secretly infidels and want to eradicate them, as well as everyone else. They're basically The Worst(TM), and should basically be smeared across the desert sands by many, many rocket launchers.
Non-Muslims don't want ISIS around, most Muslims don't want ISIS around, and even the frickin' Al Qaeda don't want ISIS around. That's right--the Al Qaeda think ISIS are too extreme and are also actively fighting against them. Let that sink in for a moment.