Some games are deliberately designed to be easy to modify, including a 'construction set' of sorts to build levels, weapons, etc., and whole modding communities spring up as a result. (Or, if the game includes any attractive women or men, nude patches.) They can be unofficial Expansion Packs (new maps or new equipment in the same game), completely unrelated games that merely use the source game's software as a backbone ('total conversions'), or just quality-of-life adjustments to the original, such as Fan Translations, bug fixes, character Cameo appearances (which can often lead to Ninja Pirate Zombie Robot scenarios), or House Rules. Game modifications, or 'mods' for short, are any alterations to a game that were not made by the game's license holder. Just because the game designers made a good game doesn't mean you can't make it even better.
