Unique

Unique is the term used in Diablo III for special, non-random boss monsters. These enemies have purple names and a line of lore below them, rather than a listing of their [[Boss Modifiers]. Such enemies were known as SuperUniques in Diablo II.

• In Diablo I and Diablo II, "Unique" referred to a type of items. Those items are called Legendary items in Diablo III.

Diablo III Boss Titles

The official boss monster terminology in Diablo III:[1]

Champions – small packs of tougher mobs that have a unique champion trait, one affix, increased health, damage, harder, etc.

Rares – single enemy of great difficulty, can have a few affixes, they’re named (randomly), much tougher, comes with a group of minions that inherit their affixes and bonuses

Uniques – Unique boss monsters. Unique name/art/skills/lairs(or specific location) and are usually a part of the story/goal of a quest, if not the actual end-boss of an act. The Skeleton King and the Siegebreaker would both be uniques.

The overlapping and changing (between games) nature of these terms is confusing to fans, and while an article and public vote on the naming conventions showed the most votes for the current Diablo III naming system, there was strong support for other naming systems as well.