In communication a code is a rule for converting a piece of information (e.g., a letter, word, or phrase) to another form. E.g., Morse code converts letters to a binary pattern, e.g., dots and dashes, allowing text to be sent over telegraph wires, flashing lights, or other channels that cannot carry speech or text directly. Another example is the use of [semaphore flags]?, where the configuration of flags held by a signaller or the arms of a semaphore tower encodes the message. Another person standing a great distance away can interpret the flags and reproduce the letters, enabling the signaller to communicate with someone too far away to hear ordinary speech. In the days when Morse code was widely used, elaborate commercial codes that encoded complete phrases into single words (five-letter groups) were developed, so that telegraphers became conversant with such "words" as BYOXO ("Are you trying to crawl out of it?"), LIOUY ("Why do you not answer my question?"), and AYYLU ("Not clearly coded, repeat more clearly."). The purpose of these codes was to save on cable costs.
Probably the most widely known communications code in use today is ASCII; it is more correctly referred to as a 'representational assignment list'. It is employed by nearly all personal computers, terminal?s, printers, and other communication equipment. It represents 128 characters with seven-bit binary numbers - i.e., as a string of seven 1s and 0s. In ASCII a lowercase "a" is always 1100001, an uppercase "A" always 1000001, and so on. Extensions to ASCII have included 8-bit characters (non-Latin letters and such things as card suit symbols), and in fullest flowering have included glyphs from essentially all of the world's writing systems - Unicode.
In cryptography a code or cipher is used to disguise the message, preventing those not in on the secret from understanding the transmission.
Acronyms and abbreviations can be considered codes, and in a sense all languages and writing systems are codes for human thoughts. Occasionally a code word achieves an independent existence (and meaning) while the original equivalent phrase is forgotten or at least no longer has the precise meaning attributed to the code word. For example, the number "86" was once used as a code word in restaurants meaning "We're out of the requested item". It is now commonly used to mean the removal or destruction of something.
In computer programming, the word code was used to refer to algorithms and has come to refer to source code.
see also country codes.
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