Rock Smash

Rock Smash is a move that can be used both outside of battles and in battles in the Pokémon video game series. It was introduced in the second generation of Pokémon games, and is primarily used to smash rocks that are blocking certain areas so that the player can progress. It can be used by tons of different Pokémon species, though in battle it's not entirely effective - a common attribute with most HM's.

In the original video game, it was named TM08, though was changed into an HM with the third generation of games, and was thus called 'HM08. In Pokémon Diamond, Pearl, and Platinum, the move can only be used outside of battle once the player comes in possession of the Oreburgh City badge, which you'll obtain from gym leader Roark after defeating his Pokémon.

Super Smash Bros. Brawl
In Super Smash Bros. Brawl for the Wii, the Pokémon Trainer's Charizard can use Rock Smash as its special side move.