Code word

1. A cryptonym used to identify sensitive intelligence data. A Code differs from a Cipher in that it operates on letter or word boundaries.
2. A word that has been assigned a classification and a classified meaning to safeguard intentions and information regarding a classified plan or operation.
3. In a code, a word that consists of a sequence of symbols assembled in accordance with the specific rules of the code and assigned a unique meaning. (e.g. Gray code).
4. A code may also be used to represent a compressed form of a word, phrase or data. (e.g. Huffman Code).

Note: Examples of code words are error-detecting-or-correcting code words and communication code words, such as SOS and Mayday. See below for details of their meanings.

Source: from Federal Standard 1037C and from MIL-STD-188 and from the Department of Defense Dictionary of Military and Associated Terms

• SOS is a general distress call used by ships and aircraft worldwide. It was created in the early days of radio telegraphy, because of its simple morse code structure ( ... --- ... ) and subsequently the backronym Save Our Souls was coined.

• Mayday, from the French m'aidez meaning simply 'help me', is a general distress call, similar to SOS, though it's generally used in voice communication.

• Roger, a term used to acknowledge a radio transmission. Can also be used in direct conversation, such as between pilot and co-pilot.

• Ten-Four, another term used to acknowledge transmissions.

• Over, a term used to indicate one is done talking. Early radiosystems used just one chanel for talking and receiving. Neither party can transmit and receive at the same time, so control of the conversation has to be handen over. This allows a rudimentary but effective form of manual Handshaking.

• Out, (over and out) a term used to end a transmission.