The Islamic State's gruesome rampage across the Middle East has united the world in horror but left it divided over how to refer to the extremist group, with observers adopting different acronyms based on their translation of an archaic geographical term and the extent to which they want to needle the extremists.

The Associated Press refers to the Sunni militant group as the Islamic State group - to distinguish it from an internationally recognized state - or IS for short, usually as an adjective before the words group, organization or extremists. Here's a brief explanation of the militant group's various names:

Read more: Associated Press