What does Sleeper mean?

Continuing Combing op,another sleeper cell busted with 11 terrorist frm banned outfit around Lhr.#indiscriminate elimination of terrorists

every woman contains the potential to gay. we are all sleeper agents that can activate if you whisper the right tegan and sarah lyric to us

.@WVUfootball is the playoff sleeper the entire country is overlooking.

#RAIL @9ja_travel: LAGOS - IBADAN BY RAIL. 2ND CLASS ----> N500. 1ST CLASS A/C---> N800. SLEEPER --> N1,200 (5HOURS) @Gidi_Traffic

#RAIL"@9ja_travel: LAGOS - ILORIN BY RAIL. 2ND CLASS-----> N1,050 1ST CLASS----> N1,600. SLEEPER---> N2,400 (11 HOURS) @Gidi_Traffic

.@YogiFerrell11 listed as an #NBADraft sleeper by @JakeLFischer (via @Sinow) #iubb

There is no other explanation: @lenadunham is a Trump sleeper agent trying to throw him the election.

Brian Hoyer to Cameron Meredith TD. Here's @AlexGelhar after calling Meredith a deep sleeper. #CHIvsIND

Infomercial sleeper 'My Pillow' gets $1 million wake-up call over false medical claims -

The sleeper of 2016: Jason Kander's breakout bid for the Senate

Is the Apple Watch a Sleeper Hit? -- @asymco says this won't be a niche product, @BenBajarin says not so fast

If Jamaal Charles can't go in Week 1, Spencer Ware shapes up to be one heckuva sleeper. Make sure he's not free in your league.

OnePlus 3T is a better version of the best sleeper Android phone of the year via @mashable

Latest entry in DNC chair race: SC's Jaime Harrison. No nat'l profile like others but a sleeper candidate to watch

#RAIL @9ja_travel: LAGOS -KADUNA BY RAIL. 2ND CLASS -> N2,350. 1STCLASS A/C-> N3,630 1ST CLASS A/C + SLEEPER--> N5,550(26 HRS) @Gidi_Traffic

The OnePlus 3T is an even better version of the best sleeper Android phone of the year

Rad Rodgers: World One has sleeper-hit potential

The best sleeper Android phone of the year just got even better

Just done the rough sleeper estimate with @arksoutreach. Encouraged that one of our long term regulars goes to residential rehab tomorrow.