MUDs tend to focus on going on quests and fighting mobs or other players to gain experience points. MUDs also offer players options for both solo and group play, so that players can have something to do even when no one else is around. MUSHes, on the other hand, tend to focus on co-operative story-telling. Given this, there’s generally no solo playing on a MUSH. The most important activity on a MUSH is roleplay and it is almost always enforced. For example, if a MUSH has a combat system, it would not be considered an IC (In Character) action to just type in the command for attacking someone. To make it IC, you would also need to write a pose describing your actions.
It is also quite common for MUSHes to have very little in the way of coded systems, and even when they do exist, they are often considered optional enhancements. It is not unusual for players to OOCly (Out of Character) negotiate the outcome of a fight instead of using code to determine who wins.
Even MUDs that enforce roleplay tend to be quite different from MUSHes. MUSHes do not have pre-set ‘emotes’ and the ‘say’ command is used very little for roleplay. Instead, MUSHers use the ‘pose’ and ‘emit’ commands, which allow for much greater variety in describing one’s actions. Examples of typical MUSH roleplay can be seen on the Logs page.