From Halopedia, the Halo wiki
Armor abilities are gameplay items featured in Halo: Reach, Halo 4, Halo: Spartan Assault, and Halo: Spartan Strike. Similar to Halo 3's equipment pieces, these items can be picked up and activated by players. Unlike Halo 3's equipment pieces, however, they are reusable. They are replaced in Halo 5: Guardians by the universally available Spartan abilities.
UNSC and Covenant armor both offer attachments that tweak the armor's performance in different ways. For Spartans, these attachments sync with the soldier's neural network to improve the armor's abilities. Similar technology has been seen in Sangheili and Jiralhanae armor with dummy modules or terminator plugs.
Armor abilities are an alteration of Halo 3's equipment. Instead of being single-use, each ability is reusable, with a cooldown time between uses. In Halo: Reach campaign, the player begins with the sprint armor ability at the start of each level, and is able to swap it with other armor abilities they may come across. In multiplayer, armor abilities can be chosen through loadouts before a match is started or during a player's respawn time. Armor abilities can be manipulated like weapons in Forge.
Most armor abilities are enabled by a small device attached to the user's lower back, with each ability displaying a different color. When not in use, these devices will project a hologram that displays the icon of the ability, allowing for quick recognition from a distance or when switching abilities. When players are killed, the armor abilities will not be dropped.
All armor abilities are rendered useless to players when transporting objects such as Flags and Oddballs. If players attempt to use an armor ability, the object simply drops out of their hands. In custom games, the cooldown time can be altered and the ability to use armor abilities while holding objectives can be added.
List of armor abilities
Halo: Spartan Assault
Halo: Spartan Strike