What does 10-4 mean in radio communication?

• A. Proceed to location.
• B. Standby for instructions.
• C. Acknowledged; message received.
• D. Emergency traffic only.

Answer: (C)

Acknowledgment of receipt is the main idea. 10-4 is used to confirm that a message was heard and understood, which keeps teams coordinated on a noisy radio channel. In fire dispatch, this quick confirmation lets the sender know the instruction or update arrived correctly, so there’s less chance of misinterpretation or missed steps. The other phrases describe what to do next or the status of the channel rather than confirming receipt: proceeding to a location is an action, standing by for instructions is waiting for guidance, and emergency traffic only flags priority on the channel. While many agencies now use plain language, the meaning of 10-4 as an acknowledgment remains a widely understood convention.