First let me state that in my unsolicited and semi informed opinion ISIS or ISIL (same group two names) is a terrorist group. Their goal is to create terror and chaos in the region and cause fear throughout the world. They post videos of their violence online for a number of reasons. Some of the most obvious reasons are: an attempt to influence the actions of the countries fighting against them, to recruit new members who aspire to such evil, lastly to terrorize everyone. They want us to cower and hide in fear.
This is the definition of terrorism from the online merriam-webster dictionary. “