"Unreleased" means something that has not been made available to the public or has not been released for sale or distribution. It refers to something that is not yet accessible or known by most people.
MomoCon has recently announced the return of SEGA's appearance to this year's convention event with panels and first playable demos of a number of unreleased games from their lineup! (segabits.com)
Normally I don't share other sites impressions of unreleased games on here. (gimmegimmegames.com)
With the world still reeling from the recent launch of Codemasters» sometimes - cute, sometimes - nightmarish Dreamworld Pogie, yet another previously unreleased game for the Nintendo Entertainment System has surfaced as a playable prototype. (gamesetwatch.com)