1. vi. To post an email message intended to insult and provoke.
2. vi. To speak incessantly and/or rabidly on some relatively uninteresting subject or with a patently ridiculous attitude.
3. vt. Either of senses 1 or 2, directed with hostility at a particular person or people.
4. n. An instance of flaming. When a discussion degenerates into useless controversy, one might tell the participants "Now you're just flaming" or "Stop all that flamage!" to try to get them to cool down (so to speak).
USENETter Marc Ramsey, who was at WPI from 1972 to 1976, adds:
"I am 99% certain that the use of 'flame' originated at WPI. Those who made a nuisance of themselves insisting that they needed to use a TTY for 'real work' came to be known as 'flaming asshole lusers'. Other particularly annoying people became 'flaming asshole ravers', which shortened to 'flaming ravers', and ultimately 'flamers'. I remember someone picking up on the Human Torch pun, but I don't think 'flame on/off' was ever much used at WPI."
See also asbestos.
The term may have been independently invented at several different places; it is also reported that 'flaming' was in use to mean something like 'interminably drawn-out semi-serious discussions' (late-night bull sessions) at Carleton College during 1968--1971.