Flaming is basically a very harsh message from one person to another via email. You can also get flamed if you participate on a mailing list, forum, group or discussion board and break the rules (or it is clear you didn’t take the time to read them).
You’ll get flamed when it appears that information that is available to you either in a manual or online, that can be found with minimal effort is not read in lieu of asking others to spoon feed it to you because you didn’t want to take the time to read it.
Flaming can also be someone just being nasty because they are having a bad day, misunderstood something you typed — or are just a plain jerk (that’s called a troll). There are a healthy amount of folks online who relish in hiding behind their screens and typing things they would never say to your face.
If you are flamed and you did break rules, or didn’t take the time to review available resources, simply offer your humble apology and the “flamer” will probably understand. The last thing you want to do is flame back when you are in the wrong — you won’t like the response to that at all.