Halo 5: Guardians will of course have a ton of competitive online multiplayer features, and Microsoft and the game's developer 343 Industries also want to make sure that the upcoming Xbox One shooter also has a vibrant online player community. To that end, they have introduced what they are calling Spartan Companies. It's basically Halo 5's version of player clans, but with a number of interesting features.
"Companies are really designed as a communal gathering place – and each Company includes its own private forum for setting up matches, scrimmage, practices, customs and Warzone sessions, as well as providing a clean, well-lit place for planning and strategy. Heck you can even find victims for your next Legendary co-op attempt."
"You can check out your Company members' stats and activity. You can customize what your Company looks like, with custom logos, colors and graphics. You can plan how your team is going to win the Halo World Championship, or simply how to avoid a chinful of Darjeeling. We'll continue to support, improve and expand Companies, and we hope you have fun with it."
Halo 5 players will only be able to join one Spartan Company at a time, at least for now.
Source: Halo Waypoint