Discs

Pokémon Radiant features Discs to teach moves to pokémon, instead of the better-known TMs and HMs. They are functionally equivalent.

There are no HM moves in Pokémon Radiant. Amazingly, pokémon trainers of the Liberti region have mastered the art of swimming! You no longer need to strap some reins onto your "beloved" pokémon simply to get to that uninhabited island; just find a beach and hop in.