Question: what do smogon tiers stand for?
Answer: Tiers are Smogon's way of categorizing Pokémon based on usage. Pokémon can be banned from the tier or move up to higher tier from their usage. ... The standard tiers that are endorsed by Smogon in Gen VI are Ubers, OverUsed (OU), UnderUsed (UU), RarelyUsed (RU), NeverUsed (NU), PU, Little Cup (LC), and Doubles.