Noun. Rubbish programs which are on television from 1am to about 6am. Nobody watches them, because most people are in bed that time, and the only ones that are up are either getting drunk in bars or working night shifts. Nevertheless, TV channels feel they must put on all of their reject programs, such as documentaries about police car chases and plastic surgery procedures.
I woke up the other night and couldn't get back to sleep, so I turned on the TV and watched five minutes of "When Penis Surgery Goes Wrong", and before I knew it, I nodded off again. Thank you, twilight telly!