Clan (social group)
From Halopedia, the Halo wiki
A clan is an organized group of players that band together for various reasons. Some battle other focused clans in an all-out clan war ("clanmatch" in matchmaking) in team games and for practice. Other clans consist of members who share a common interest, such as machinima production or Forging.
Clans are primarily social structures and as such, they exist in all three of the Halo first-person shooters. They are becoming less prevalent in the older games, particularly Halo: Combat Evolved. In Halo Custom Edition, however, clans are still easy to find; they host multiple dedicated servers in an effort to provide places for people to play -- and, of course, to boost their "publicity".
There is no built-in clan ladder on Halo 3. This has led to the development of numerous informal ways to identify with a clan; clan members often share the same emblem or service tag. Clans organize externally, coordinating and recruiting on websites and Bungie.net. The much larger communities of gamers are sometimes devoted to other games in addition to Halo; they also tend to be more competitive. Examples include Major League Gaming and LCU, the two largest Halo 3 gaming communities in the world. To survive, such clans tend to keep a close eye on their members' gaming activities; hold meetings; raise money to fund the community and the websites; and constantly recruit in an effort to maintain the clan's popularity and longevity.
In Halo 2
The Halo 2 clan system has a ranking system that consists of the following:
In Halo: The Master Chief Collection
A clan tag will become available after completing 50 multiplayer games or campaign missions.