I'd just like to clarify the difference between clan and party
a party is a group of people who are online and you are with, parties are temporary groups of players, that generally help eachother out, such as heal eachother and kill bosses together.
a clan/Guild is a semi permanent, part of a game, clans work hard to support eachother and make everyone in the clan better at the game and have better equipment. Clans can enter tournaments in some games. Clans are not the same as a party, a clan you stay in even when you log out, a party you generally leave the party when you logout with most games.
Clans are like gangs/corporations they have a hierarchy of players a leader, maybe some officers, then the general members
Parties generally consist of between 2 and 10 players in most games and may have a party leader, parties are a temporary way to help eachother out, in some games Parties get a special chat room.