Ten Codes are sets of numbers beginning with the number 10 and used — originally by police — as a form of shortened communication. There are dozens of code combinations, depending on where ...

In a June 1935 issue of the Association of Police Communications Officers (APCO) Bulletin, a suggestion was made to create a set of "brevity codes" based on procedure symbols used by the U.S. Navy.

The 10-code system varies by jurisdiction. Even in the Quad-Cities, the 10-codes mean different things at different departments.

Meaning acknowledgment or okay, “10-4” comes from the 10 Codes list that emergency personnel use to communicate with each other, commonly done over the radio.