Ten-code

Ten-codes are the code words used by law enforcement officials and radio operators. They were introduced in 1937 by a man in the Illinois State Police, who got frustrated over the fact that radios at the time took about a tenth to a fourth of a second to "spin up." So adding the word ten would allow enough time for the radio to send the signal clearly.

The most famous ten-code is 10-4, which means "OK."

But the federal government recently suggested that the ten-codes should be phased out in favor of plain language, since different agencies have different meanings for a number of codes.