Server Emulators and Private Servers,

What is a private server?

Private servers run either emulated or re-engineered versions of a game's server side software.  This allows nearly anyone with sufficient technological skill to run their own virtual world and community.  Admins can change nearly any aspect of the game, including XP rates and Loot drop frequencies.  Servers usually run a specific patch version of the game, requiring clients to patch to that specific version.

You either love them or you view them as the gaming equivilent of a unibrow.  It's true that many gamers hate private servers, seeing them as cheap and robbing legit servers of community members.