Other mistake: When we first see the Saito Gemu HQ, the shot is mirrored. It is apparent by the reversed company logo sign. (00:14:25)
Rachel, Jack and Ashley Too - S5-E3
Continuity mistake: As Catherine is walking up the stairs, an extra shadow in the light from the skylight moves. In the next cut the moving part of the shadow is gone. (00:07:20)
Continuity mistake: When Nida is chasing Smart in her car, they are (correctly for England, in which it is set) driving on the left until they reach the level crossing. After they cross the level crossing, they are both seen driving on the right, with Nida trying to overtake Smart on the left. This has nothing to do with changing lanes during a chase, as Smart is, at that stage, unaware that he is being pursued.
Continuity mistake: The way Kenny holds the gun during the robbery changes between shots with no time for him to adjust his grip. He goes from holding the gun using his right hand with his left hand wrapped around his wrist, to holding the gun with both hands. (00:37:49)
Answer: It's a derogatory slang term made up for the show.