It can be pretty much anything you want. Some are reports on what happened in peoples games. Others are fiction based on their games, while others are complete fiction.

No problem. If you want examples of fiction, you can check out my story, Jordan's Revenge. 

After Action Report

Initially, AARs, or after action reports, were really just that; a report on a game that someone had played complete with pictures and/or maps. Eventually this grew into people building up fiction around their games. For most games this works out rather well, but beware, starting an aar and seeing through to its complete end is more work than you may think. Often a writer is torn on waht to include and what to leave out of the story. one doesn't want to make the story dull and boring and at the same time you want to include as much detail as possible to make sure your reader gets an accurate portrait of the universe created within your aar.

cheers