HM

From Bulbapedia, the community-driven Pokémon encyclopedia.

A Hidden Machine, usually abbreviated HM (Japanese: ひでんマシン Secret Machine), is a machine used by Pokémon trainers to teach a Pokémon a new technique, or move that it would not otherwise learn. All HM moves are usable out of battle (though the reverse is not true), and most are essential for completing the game. Whereas TMs are good for only one use, HMs can be used over and over again on many different Pokémon. However, there is a disadvantage to the infinite uses: a move learned through an HM cannot be forgotten without the aid of the Move Deleter. In addition, Pokémon with HM moves cannot be transfered from a Generation III game to a Generation IV game via Pal Park, and so the HM move must be deleted before the transfer can take place.

A mutually compatible HM move be passed down through breeding with the male Pokémon passing down moves in the egg groups, much like mutually compatible TMs can be. As of Generation IV, only five Pokémon learn an HM move through leveling up.

Although HM moves are necessary to complete the games that they are HMs in (except for Flash, Fly and Defog, as well as Cut in Hoenn-based games, though they are very helpful), many of them lack usefulness in actual Pokémon battles. Thus, players often capture extra Pokémon to keep in their parties solely to use most of the HM moves.

The original five HMs remained the same from Generation I up to Generation III, as in Generation IV, Flash was moved from its position as HM05 to TM70, leaving the space open for Defog. What remains true, nonetheless, is that all HMs except for HM05 contain damage-dealing moves in every generation released so far. Strangely, the Generation IV HMs are all Physical moves except for Surf and Defog.

The English name, Hidden Machine, is a pun on the Japanese name, ひでんマシン (Hiden Mashin). Hiden means "secret".

For their in-game locations, see Locations of TMs.