To insult someone electronically, or otherwise. Sometimes to be a group insult.

The l4m3 k1dd13 finds himself flamed. UserA:hay ne1 gots sum wareZ ?!@#!@# I wanna h4x0r my momz yahoo account!! UserB: You're a tard... seriously. Do yourself a favour and get out of the gene pool.

To insult a person you are arguing with over the internet in hopes of reviving your argument.

You are an idiot for thinking this.

A flame is noun associated with the action of flaming, what people do when they express a strongly held opinion without holding back any emotion. Although flames often get out of hand, they have a purpose in the ecology of cyberspace. Many flames are aimed at teaching someone something (usually in overstated language) or stopping them from doing something (like offending other people). Flame messages often use more brute force than is strictly necessary, but that's half the fun. Netiquette does ask that you consider the art of flaming before pulling out the flame-thrower.

A famous flame by Linus Torvalds "This 'users are idiots, and are confused by functionality' mentality of Gnome is a disease. If you think your users are idiots, only idiots will use it. I don't use Gnome, because in striving to be simple, it has long since reached the point where it simply doesn't do what I need it to do." (...) "Gnome seems to be developed by interface nazis, where consistently the excuse for not doing something is not 'it's too complicated to do', but 'it would confuse users'."

a flame is a tirade. The flamer may be quite articulate and intelligent as they question the upbringing of the flamee. One can also flame about a third party to a conversation. Finally, a flame may be from an idiot, in response to a resonable post from someone else.