10-4 (slang for "acknowledged")

"10-4" is a term from radio communication slang, originating from the ten-codes used by law enforcement and CB (citizen band) radio operators. It means "acknowledged," "understood," or "message received." When someone says "10-4," they are indicating they have received and understood the message. It’s a quick, concise way to confirm communication without needing lengthy explanations. While commonly associated with CB radio culture, it’s also used in various professional settings, such as emergency services and logistics, to streamline and clarify communication.