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.