World War III:
1) A war which involves the whole world (or most of it, including all of the major countries). It is often predicted but hasn't happened yet.
2) A slang term, meaning a huge fight or 'disaster zone' (both literal or figurative).
NOTE: This is often shown as "WWIII"
1) "If the present world situation doesn't change soon, we'll have WWIII"
2) "OMG It looks like WWIII in here!" ...OR "They're about to have WWIII"