Cut

Cut is a -type physical move introduced in Generation I. It has been HM01 since Generation I.

In Battle
Cut can target any Pokémon adjacent to the user. Cut does damage to the target.

Outside of Battle
Cut enables a Pokémon to cut down small trees that may be blocking the player's path. Prior to Generation IV, Cut could cut down tall grass as well, though in Pokémon Emerald, a Pokémon with the ability Hyper Cutter cuts down the most tall grass in its use.

Trivia

 * In Pokémon Black and White, Cut is the only HM required to be able to complete the game, despite the player receiving other HMs throughout the course of the game.
 * You also need it in FireRed and LeafGreen so you can get to certain gyms, i.e. Celadon Gym.