From Halopedia, the Halo wiki
Bosses also known as boss battles make several appearances in the Halo series. When a character who is a major antagonist appears in gameplay, they often appear as boss fights against the player.
List of bosses
The following is a list of boss fights throughout the Halo games.
Bosses in campaign are often enemy characters with more health and typically a mechanic or strategy to effectively take them down.
Bosses in the Warzone gametype come in three different types. Killing a standard (white icon) boss results in a Boss Takedown and 25 VP, while killing a Legendary (yellow icon) boss gives a Legendary Takedown medal and 100 VPs, and killing a Mythic (red icon) boss gives a Mythic Takedown medal and 200 VP.