Board Thread:Roleplay/@comment-33989872-20180408053939/@comment-33989872-20180410113317

Oak: TM stands for Technical Machine. Pokemon Trainers can give these CDs to their Pokémon to help them to learn new moves to use against opponent Pokémon. In Pokémon Generations 1-4, TM's could only be used once, and then they disappear. Recently, though, Pokémon Black and White allowed players to use them more than once. (Got that from the wiki)