OU

“OU (OverUsed) is Smogon’s fundamental usage-based tier. With the exception of Pokémon banished to the Uber tier, every Pokémon can be used in OU, including Pokémon from UU, RU, NU, and PU. While all non-Uber Pokémon can be used in OU, only those Pokémon that make up at least ~4.52% of total weighted usage in the tier are designated OU. A Pokémon is truly OU if a typical competitive player is more than 50% likely to encounter that Pokémon at least once in a given day of playing (15 battles).” -Smogon.com