A code word is a word or phrase that is used to convey a predefined message that differs from its own literal meaning. For example, the code word IRONBOUND might be used to convey the message "meet by the river at midnight." If a number (e.g., 785) is used instead of a word, it is termed a code number. Both code words and code numbers are also termed code groups.
A code is comprised of a list of messages and the code groups that have been defined for them, usually written down in parallel columns in a codebook. To create or interpret messages in a code, one must have access to its codebook. One advantage of a code, as compared to a cipher, is that a single code group may contain a variable amount of information, even within a single code; the code word IRONBOUND, above, conveys a complete command, while another code word might stand either for a single word or for an entire plan of operation. This makes a well-designed code difficult to crack by examining captured messages for patterns.
Word codes, however, also have disadvantages. First and foremost, if a copy of the codebook falls into enemy hands, then the code becomes useless. Second, only ideas for which code words have been predefined can be communicated using a given code. For example, if a code book contains no code word for "noon," it may be impossible to convey the message, "meet by the river at noon." Codes are therefore limited in flexibility by the number of code words that can be fit into a code book of practical size, whereas ciphers can convey almost any written message.
█ FURTHER READING:
Mollin, Richard A. An Introduction to Cryptography. New York: Chapman & Hall, 2001.
Singh, Simon. The Code Book. New York: Doubleday, 1999.