Unused content refers to information found in the coding of video games and related media that are not used. It is sometimes referred to as 'beta information', although this can be a misnomer because the content may not have necessarily been added when the game was feature complete, and due to differences in opinions on what makes something 'beta'. It is a specific form of prerelease information, but not all kinds of prerelease information are unused content.
Unused content may give insight into the game's development. Sometimes the unused content may have been intended to have been added to the final game, while other times it may be added for development purposes only, such as the the Trainer and Pokémon color debug menu in Pokémon Gold, Silver and Crystal.