Finally Halo 5: Guardians is getting it's own version of the Infection game mode that has been popular in Halo since Halo 3. A custom gametype called Zombie which gained a large following during the Halo 2 days is where the Infection game mode was truly born however.
In Infection, the game starts with the majority of players on the 'human' side. A small selection of players, usually just one or two, are considered 'infected' and they must hunt down the human players. If an infected player kills a human, the human will then respawn as an infected. In nearly all cases, all players are usually infected before the time runs out.
The infected players are equipped with fast movement and a glowing green energy sword, whilst by default the human players will have the shotgun and the magnum at their disposal.
343 Industries has slowly been adding new game types to Halo 5: Guardians since it's release and the latest Infection game mode will be added alongside the Ghosts of Meridian update.
The new Ghosts of Meridian update will also add a number of other features and gameplay content, on top of a variety of new cosmetic items that will be available within REQ packs. Perhaps the biggest new addition to Ghosts of Meridian, besides the new infection mode, will be the Tyrant game map. Unlike most other new maps, Tyrant has been built completely in-house and has not been built within forge.