ROM hacking is the process of modifying a video game ROM image to alter the game's graphics, dialogue, levels, gameplay, or other gameplay elements. This is usually done by technically-inclined video game fans to breathe new life into a cherished old game, as a creative outlet, or to make essentially new unofficial games using an old game as a foundation.
ROM hacking is generally accomplished through use of a hex editor (a program for editing non-textual data) and various specialized tools such as tile editors, and game-specific tools which are generally used for editing levels, items, and the like, although more advanced tools such as assemblers and debuggers are occasionally used. Once ready, they are usually distributed on the Internet for others to play on an emulator.
Fan translation (known as "translation hacking" within the ROM hacking community) is a type of ROM hacking; there are also anti-censorship hacks that exist to restore a game to its original state, which is often seen with older games that were imported, as publishers' content policies for video games (most notably, Nintendo's) were much stricter in the United States than Japan or Europe. Although much of the methodology applies to both types of hacking, this article focuses on "creative hacking" such as editing game levels, TheShinyMew is facinated with ROM-hacks on Pokémon.