An outspoken dispute in a public forum such as a news group or email list, with usually about half a dozen fierce combatants.
Reason and logic seem to go out the door, and "ad hominem" attacks are plentiful. GodwinsLaw is sometimes (unwittingly) adhered to.
One famous flame war was opened by AndrewTanenbaum (a well-known ComputerScience professor who wrote many books about, among other topics, OperatingSystem design, as well as writing much of Minix) by a posting with the subject "LINUX is obsolete". See if you can spot any hostile language in this brief quote from Linus' first reply:
Re 2: your job is being a professor and researcher: That's one hell of a good excuse for some of the brain-damages of minix. I can only hope (and assume) that Amoeba doesn't suck like minix does.