HM

A Hidden Machine, HM for short is an item that, like a TM, is used to teach a Pokémon a move.

The difference between a TM and an HM is most pronounced in the earlier games in the series, where TMs were single-use items while HMs could be used an unlimited amount of times after they were obtained. HMs, unlike TMs, could not be sold for money, and the moves contained within could not be forgotten by Pokémon under normal circumstances. An HM move could be used by Pokémon even if they had fainted during battle.

All HM moves have the ability to be used outside of battle in the games they are HMs in, though a move's ability to be used outside of battle does not mean that it is necessarily an HM move. To be used outside of battle, specific Badges must be obtained by the player prior to Generation V to advance the game's storyline.

Generation WTI
There are six HM items obtainable in the Rikoto Region, each of them substitutes for one of the HMs. You may also buy each of the HMs in Greenpine City for 20000 as well, these function as stated previously.