phrase origins

[wgraefe]

Where and when did the expression "ten-four" originate?

[sft42]

10-4 is CB (citizen's band) Radio shorthand......meaning everything is all right.....there are quite a few of them 10-10 means basically the same as over and out.

[Quizmonster]

I believe such things started life as police radio code. If you click here, that will link you to a web-page which lists pretty well all of them, including 10-4.