Chicago Transit Authority Final Qualification Practice Test

In radio communication, "10-4" is a part of the ten-codes, which are brevity codes used to convey information succinctly, especially in law enforcement and emergency services. Specifically, "10-4" means "message received and understood." This code is universally recognized across various radio communication settings, allowing for a clear and efficient acknowledgement that the message has been grasped.

Using standardized codes like this helps to minimize misunderstandings and ensures that crucial information is transmitted quickly and accurately among operators, especially in situations where clarity is essential. The other options refer to different meanings, but "10-4" specifically denotes acknowledgment, making it a vital part of communication protocol in radio operations.