Mud - (Multi User Dangeons) is text based roleplaying game that can be played over the internet.You send some commands to the mud server and you get reply it after short time. It looks like old roleplaying text games. The most significant difference is that you can play with many people all over the world (ie. few hundreds). Second difference you will notice when you try to visit all world. It's imposible because the world is growing and becomes larger and larger.