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)
San Junipero - S3-E4
Continuity mistake: Near the end, Yorkie gets into a red left-side drive convertible, then is seen driving on highway in the same car but with right side drive. Following scenes are of a left-side drive car. (00:58:00)
Continuity mistake: While mother and daughter are at the park, when the mother looks at the girl a train is passing on the tracks next to the park, but when the camera switches to the mother there is no train, then when it switches back to the girl the train is there again.
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.
USS Callister: Into Infinity - S7-E6
Continuity mistake: The crew inside Nanette's head sees what she sees. In the hospital, when she looks in the mirror, they correctly see the reverse image of her face. She has a big wound on her right cheek, which should appear on the left when mirrored. In subsequent shots, however, the crew sees the wound on her right cheek, which is on the wrong side if they are seeing her image in a mirror. It's as if they recorded Cristin Milioti looking directly into the camera for these shots but forgot to flip the image. (01:22:10 - 01:23:41)
Answer: It's a derogatory slang term made up for the show.