Power-up

"Power-ups" give you an advantage over the other players in a multiplayer battle in Halo: Combat Evolved, Halo 2 and Halo 3. On a few occasions, they're also found in Campaign, though they are only available in Halo 3 as invincibility, which is technically counted as an equipment piece. You activate them as you walk into them, unlike equipment which is not activated instantly, and they can not be held like equipment; they are instant, one-time uses.

Trivia

 * The Custom Powerup's default settings increase your speed and melee power. It has been speculated this was to be the effects of a unused Agility Powerup.