Definition - What does Flame mean?
A flame is an insulting and hostile comment made by one online poster against another user in an online setting. This commonly happens in forums, message boards, game lobbies or any place online where people with different beliefs and principles gather. A flame usually occurs as a result of debate on heated topics such as religion, philosophy, politics and gender.
Techopedia explains Flame
Flames are simply comments or messages designed to offend the user at which they are directed. The resulting tirade from both parties is known as a flame war. Some people deliberately say something to initiate flame wars in forums and message groups. The comment doesn’t even need to be intelligent; an obvious blunt remark or something aimed at another user's ego will often do. People who flame others are called "trolls."