What is loot specialization in WoW?
It will prioritize the type of gear you want to see when looting bosses and mobs.
Loot Specialization is a feature introduced in Patch 5.3 which allows players to set the loot priority for their character to favor a particular specialization. This loot priority setting only affects bonus rolls, Raid Finder loot, World Bosses loot and Heroic Scenario loot. This feature was primarily added to allow players to collect off-spec gear.
https://wowwiki.fandom.com/wiki/Loot_Specialization