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1.
A sleeper cell is a person who remains a dormant member of a group while belonging to another group for undisclosed reasons. Usually the sleeper cell status is kept a secret.
Those terrorists pretending to be normal students were the ultimate sleeper cells.

Why didn't you tell me you were half Asian? You're such a sleeper cell!
 
2.
A girl or boy who was very unattractive in high school and has otherwise become unbelievably hot in college or beyond.
Oh my gosh Josh is such a sleeper cell! He was never even remotely cute in high school.. Now look at that!
by Red1920 July 24, 2014
 
3.
When a buddy is hanging with you and starts talking to a girl, then throws you under the bus to try and get some from her. He turns his back on his boys to further the chase.
Jake just went sleeper cell on me and Jethro at the bar to get after the married chick.
by bigdust13 January 12, 2010
 
4.
Suffolk based band best known for their performances on Channel 4's Orange Unsigned Acts. Known for their pop-punk sound and great sense of humour, the boys were well loved despite lack of support by the show's judges.
Original line up saw Barnaby Courtney (lead Vox), Kyle Orton (Guitar &Vox), Patrick Richardson - Todd (Lead Guitar), Rob Banthorp (Percussion) and Matt Fowkes (Bass) wow audiences up and down the country with their catchy riffs, great harmonies and synchronised jumping!

On the show, only Barnaby and Kyle seemed to be allowed to open their mouths (Which most people found appalling due to the humour seen from the rest of the boys in their video diaries) and some obvious editing put them at each others throats, while the rest of the boys were just shown to look "worried".

After the show, the pressure became too much for lead singer barnaby and he left the band in the lurch just when us fans needed him the most. Thousands of young girls were devastated, although this did leave room for Pat & Rob fans to take the lead.
The band carried on for another year, playing a range of gigs up and down the country to receptive audiences and new fans.

As far as i know all members of the band are in a relationship but when that changes Patrick is mine!
"Did you see sleepercell play at the strawberry fair? I did, it was awesome!"
by totalposer January 21, 2010
 
5.
this happens when you stay the night at someone's house, and the next morning while in the shower; you accidently cum on the louffa hanging from the faucet.
"she doesn't know how she got pregnant, must have been a sleeper cell"
by 1/2RICAN November 11, 2009