Tier 8 sets are 5-item, class-specific sets that can be acquired by raiding Ulduar. Separate 10-man and 25-man versions of each set exist, sometimes referred to by players as "tier 8.10" and "tier 8.25" (or "tier 8" and "tier 8.5") respectively. 10-man sets are all prefixed with "Valorous", while 25-man sets are all prefixed with "Conqueror's". No matter which level of tier 8 is worn, all pieces count toward the same set bonuses.
The items that form these sets are purchased with tokens which drop from various bosses in Ulduar. For details, refer to the set page. Note that the bosses drop tokens for different slots depending whether 10-man or 25-man mode is enabled.