A "sleeper" is a person or thing that seems ordinary or unremarkable at first, but then unexpectedly turns out to be very impressive, powerful, or successful. Full definition
There is also an additional queen sleeper sofa in the living room. (luxuryretreats.com)
Spacious king size or single en - suite room with sleeper couch for a child. (travelground.com)
Smaller, more personal works might make a modest profit while cruising the art - house circuit in the hopes of becoming sleeper hits, though that's, of course, a gamble. (chicagoreader.com)