A phrase from two-way radio. It combines "Roger" (meaning "Received") and "Wilco" (meaning "will comply"). The letter R had been phonetic alphabet shorthand for "Received", and over the radio it became "Roger". In the military, Roger and Wilco are used exclusively. Basically it means I hear you and will comply with your wishes or command.
air traffic controller: we have had reports of severe thunder storms near you at 22000 feet. reduce altitude to 18,000 feet.
Wife: Honey pick up some milk on the way home.
Husband: Roger wilco
pilot: roger wilco