Characters of CthulhuMud
Characters represent human players within the mud. Characters are also mobs (mobile objects) within the mud and are subject to the same restrictions. Each character has a number of attributes which describe it and make it different from all of the other characters and mobs. The most important of these being its name.
Characters are the agents through which humans interact with the mud. Some systems refer to characters as Avatars.
A mob is a mobile object. That is to say it is an object within the mud that can move around and do a number of things that 'living' creatures can. Mobs are used to simulate living creatures within the mud.
Most mobiles are controlled by the software, generally using very simple raction based programming. Attack a mob and it will fight back. Some mobs are more sophisticated and can interact in more interesting ways.
Player Characters (PCs)
A player character (PC) is a mobile whose actions are controlled by a human (or atleast an entity on the other end of a TCP/IP connection). Messags describing what the mob 'sees' are sent to the player, and his instructions (commands) are sent back to the mob which tries to execute them.
In the future, as clients get more advanced, the mud may be modified so it can send events to the players client, rather than simply messages. The advantage is that it gives the client more information, the disadvantage is that the client has to be coded to understand the events.
Non Player Characters (NPCs)
This term is sometimes used to refer to mobiles within the mud. Strictly speaking it should only be used for the more human or more developed mobiles, as it originates from the AD&D system, where NPCs were 'monsters' created using the player character system, rather than the monster system.
In terms of implementation, there is no difference between an NPC and a normal mobile.
You control a character within the virtual world. As a character of that world there are certain things he is expected to know and certain things he is not. This knowledge is probably very different from what you, as the player, know. The character is also expected to behave in certain ways, both due to their class, race and position in society but, after a while, because of the way that the character has previously behaved.
When you start playing, the characters options are fairly open. Your character will have a profession, an alignment and a gender. The abilities of the character are the biggest limitations on how you behave. Although you might want to kill the dragon, it may have other ideas about the matter. If it is tougher (more able) than your character, then the result of you telling your character to attack the dragon will be that the dragon gets a nice crispy snack.
Other behavioural modifiers may come from gods and societies, all of which have some rather firm ideas about how their followers or members should behave. Societies are likely to expel members who misbehave, while gods are known to favour less subtle approaches involving lightning bolts.
As you character does things within the mud, it will gain experience and its abilities will increase. Levels and skills are the most obvious signs of the characters increasing abilities. Levels give the character more hit points, more mana and make it a little better at several things. Skill increases make the character better at specific tasks. You can control your characters skill development, to some extent, by choosing which skills they should paractice.
In Character (IC) vs Out Of Character (OOC)
If you are interacting with the world just in terms of your character and the part of the world that you are in, then you are playing In Character.
If you are interacting with other players in ways unrelated to the world (such as chatting about homework or football), or you are interacting with parts of the world your character could not reach then you are playing Out Of Character. While some OOC playing is inevitable, it does disrupt the IC experience for those players who are trying to get into the role playing aspects