Its a private server for MW2, that has been modified a little from the original version to support the console, dedicated servers, and a little more customability. It has a few other things that make it good, but overall, the dedicated servers are the biggest plus.
Lols yeah what everyone else says. I am just going to assume it stands for: Alternative Infinity Award Net. It's a large private server community for Modern Warfare 2. You can host your own dedicated servers here, play with hundreds of different custom mods, and more.