The term "10/4" is part of the ten-codes used in radio communication, particularly among law enforcement and emergency services. It signifies acknowledgment or understanding of a message. When someone says "10/4," it means they have received and comprehended the information conveyed. Originally developed in the 1930s, these codes help streamline communication and reduce misunderstandings. The use of ten-codes, including 10/4, became widespread in the CB radio community and is still popular today among truckers and hobbyists for efficient communication on the road.