A WAD file, an acronym for 'Where's All the Data', is a container file format primarily used by id Software's video games, most famously Doom and Doom II, but also by other games like Heretic, Hexen, and Strife. It serves as a package for various game assets, including maps, levels, sprites, textures, sounds, music, and other game-related data. The WAD format is essentially a collection of 'lumps' (individual data blocks) preceded by a directory that specifies the name, offset, and size of each lump within the file. There are two main types: IWADs (Internal WADs), which contain the core game data and are required to play the game, and PWADs (Patch WADs), which are user-created modifications or add-ons that patch or extend the original game content. This modular design allowed for extensive modding and community-created content, significantly contributing to the longevity and popularity of games like Doom. While newer game engines have moved to more sophisticated archive formats, the WAD format remains iconic and is still supported by modern Doom source ports.