In commercial aviation, a red-eye flight is a flight scheduled to depart at night and arrive the next morning. While any overnight flight may be considered a red-eye, the term is most commonly used for west-to-east flights that take advantage of time differences in order to move passengers long distances without the loss of a business day. For example, in North America red-eye flights typically depart from the West Coast between 10:00 p.m. and 1:00 a.m. and arrive on the East Coast between 5:00 a.m. and 7:00 a.m. the next day. Due to local time changes and the short overnight flight duration, passengers arrive on the East Coast at the beginning of the next day without having adequate time for a full night sleep.

The term "red-eye" derives from the symptom of having red eyes, which can be caused by fatigue or late-night travel.

https://en.m.wikipedia.org/wiki/Red-eye_flight