World Events are activities that appear in public areas, and change with each new expansion. Completing world events yield rewards to the player.
The Dark Below: Blades of Crota
The World Event for The Dark Below was that every ten minutes or so on Earth or the Moon, the Hive would summon a Blade of Crota. Killing the blade would drop an Ascendant Sword that the player could use to kill the Hive that would spawn shortly after. This event counted towards two of Eris Morn's daily bounties.
House of Wolves: Wolf Packs
House of Wolves reintroduced the Queen's Wrath, retooled as a bounty hunter activity in which players could collect bounties on Fallen targets that would arrive by Skiff to public areas on Earth, the Moon, and Venus. These fallen always came in waves; the first wave would drop a small group of Fallen and two Scorch Captains. Killing the first wave would initiate five more waves; on the last wave, the Bounty target, typically a Wolf noble, would appear. Killing the target would not only complete the bounty, but also cause an Ether Chest to appear somewhere in the area. The player had one minute to find the chest and unlock it for ammo synthesis, planetary materials, and a chance at a Treasure Key.
The Taken King: Taken Lieutenants
In The Taken King, Taken will periodically certain areas. Certain of these Taken are Lieutenants; usually they are Captains, Knights, Minotaurs, or Centurions. Killing three Lieutenants before the Taken retreat will summon a Taken Champion, an Ultra-level enemy. Killing the champion is a requirement for certain Taken War quests, and have a chance to drop Runes, as well as Relics that can be returned to Banshee-44.