A change key is a key on the lowest level of a master keying system. Change keys are also referred to as day keys. Typically change keys are issued to personnel that require access to one or two areas in a facility. By definition, a change key is not a master key.
Change key can also refer to the specialized keys used to change the combination setting of a combination lock.
Change key can refer to a special key on the "Sabre" Keyboard, located to the right of the "P" key, and can also be typed by doing ALT+0164, or using '@' in Turbo Sabre. Sabre is a Global Distribution System (GDS), used by travel agencies to book flights, hotel reservations, car rentals, etc.