What does the acronym UM refer to in aviation?

The acronym UM in aviation stands for "Unaccompanied Minor." This term is used to describe a child who is traveling alone without a parent or guardian. Airlines have specific procedures in place for unaccompanied minors to ensure their safety and comfort during the flight. These procedures typically include special check-in processes, dedicated staff attention, and assigned seating to help facilitate a smooth travel experience for the child. Recognizing the needs of unaccompanied minors is important for airlines, as they bear an additional responsibility for the minors' well-being throughout their journey.

The other terms provided do not relate specifically to aviation protocols or procedures for minors traveling alone.