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In telecommunication, a code word is an element of a code. Each code word is a sequence of symbols assembled in accordance with the specific rules of the code and assigned a unique meaning (e.g. a Gray code).^[1]

Contents 1 Coding Theory 2 Cryptography 3 Radio communication procedure words 4 Footnotes 5 See also 6 External links

Main article: Coding Theory

Coding Theory is the branch of mathematics that covers source codes and channel codes.

A channel code contains redundancy to allow more reliable communication in the presence of noise. This redundancy means that only a limited set of signals is allowed: this set is the code.

A source code is used to compress words (or phrases or data) by mapping common words into shorter words (e.g. Huffman Code).

Main article: Cryptography

Cryptography is about the creation of ciphers. A code word is an element of a code book designed so that the meaning of the code word is opaque without the code book.

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

• 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, or Save Our Ship was coined.

• Mayday is a general distress call, similar to SOS, though it's generally used in voice communication. It was developed from the (grammatically incorrect) French m'aidez, meaning simply 'help me'. Do not use the keyword MAYDAY unless you are aboard a vessel or aircraft which is in immediate danger of sinking or crashing.

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

• WILCO, means "I have received and understood your message and will comply (Only used by the addressee)"

• Say Again, a term that requests the sender repeat all of the last transmission. ('Repeat' should not be used for this purpose, as it is used to request a second, identical artillery barrage.)

• Words Twice, requests the sender to double the pronunciation of each word. eg. I I have have your your dog dog. Usually used when the signal is poor.

• SitRep, Lit. 'Situation Report'. Eg. 'What's your sitrep?' or 'Sitrep to follow'. Sitrep will include information on position, movement status, direction of move, casualty status, etc.

• Over, a term used to indicate one has finished talking, and implies a response is expected. Early radio systems used just one channel for talking and receiving. Neither party could transmit and receive at the same time, so control of the conversation has to be handed over. This allows a rudimentary but effective form of manual Handshaking.

• Out, a term used to end a transmission (never properly used with OVER).

• Ten-Four or "10-4", another term used to acknowledge transmissions. It is one of the Ten-codes made popular during the CB craze of the 1970s.

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• Safeword
• Password
• Marine VHF radio
• Euphemism
• Error correction and detection
• Code name
• Classified information in the United States

• UNHCR Procedure for Radio Communication