"Unlockable content" refers to extra features, levels, or items in a video game that you can access by achieving certain goals or progressing in the game. Full definition
Even though Legend mode's story line is the same as its predecessor, it is clear to see that Koei have spent a considerable amount of time on the game mechanics and the amount of unlockable content in the game. (plusxp.com)
There's also plenty of unlockable content in the game and Sony have reported that additional DLC characters will be available. (impulsegamer.com)
New enemies, difficulty options and unlockable content make Redux the definitive version of the game. (xboxgamerreviews.com)