What is a class? What is a guild?
In general, a class is a grouping of players with common abilities. A guild as well can be said to have the same definition. Many muds, if they use either of these concepts at all, add some very individual nuances. To muds which do not have classes or guilds, the concepts are naturally irrelevant. Those which have one or the other are often using the terms in an interchangeable fashion. Finally, those muds which have both often define class in a more generic manner than guild. For example, on Nightmare, a class is like a profession and the guild like a particular job. You might have people in the fighter class who are in the templars guild, and others who are in the rangers guild. In short, the guild is a way of specializing your class abilities. Other muds allow “multi-classing”, which may mean joining multiple guilds, classes, or both. It is always best to check out the “help guild” and “help class” command on any given mud to see how it defines these terms.