Used to change the description of your room; it will be displayed to users when they request the room information with the info command.
Example:
/msg chanserv set #webchat desc the dragon room
Like the topic, some people may use the description to decide whether they wish to join the room. However, the description can only be set by the founder, and is generally changed less often than the topic. Most people expect the description to give some information about the purpose of the room.