"Unlockable extras" refers to additional features or content that can be obtained in a video game or other software program by meeting certain conditions or achieving specific goals within the game. Full definition
The game features four different cups consisting of 20 challenges each, plus a large number of unlockable extras like more tracks, car upgrades, new racers, and more. (allpcgame.net)
Beyond multiple playable characters, over 100 levels and secrets; Toolkitz Games has emphasised replay value in Magical Star Pillars» gameplay mechanics including unlockable extras such as concept art and behind - the - scenes development videos. (gamingtrend.com)
One thing... There are five unlockable extras in Enemy Mind that we haven't publicized much and a couple of them are pretty meaty. (gameramble.com)