A code name or cryptonym is a word or name used clandestinely to refer to another name or word. Code names are often used for military purposes, or in espionage. They may also be used in industry to protect secret projects and the like from business rivals.

In the First World War, code names common to the Allies referring to nations, cities, geographical features, military units, military operations, diplomatic meetings, places, and individual persons were agreed upon, adapting pre-war naming procedures in use by the governments concerned. In the British case code names were administered and controlled by ISSB (The Inter-Services Security Board) staffed by the War Office with the word list generated and randomised by GC&CS (later GCHQ). This procedure was coordinated with the USA when America entered the war. Random lists of code names were issued to users in alphabetical blocks of ten words and were selected as required. Code words became available for re-use after six months and unused allocations could be re-assigned at discretion and according to need. Capricious selection from the available allocation could result in clever meanings and result in an aptronym or backronym although policy was to select words that had no obviously deducible connection with what they were supposed to be concealing. Those for the major conference meetings had a partial naming sequence referring to devices or instruments which had an ordinal number as part of their meaning, e.g. the third meeting was "TRIDENT." Joseph Stalin, whose last name means "man of steel", was given the code name "GLYPTIC," meaning "an image carved out of stone."

A code is a rule for converting a piece of information (for example, a letter, word, phrase, or gesture) into another form or representation (one sign into another sign), not necessarily of the same type.

In communications and information processing, encoding is the process by which information from a source is converted into symbols to be communicated. Decoding is the reverse process, converting these code symbols back into information understandable by a receiver.

One reason for coding is to enable communication in places where ordinary spoken or written language is difficult or impossible. For example, semaphore, where the configuration of flags held by a signaller or the arms of a semaphore tower encodes parts of the message, typically individual letters and numbers. Another person standing a great distance away can interpret the flags and reproduce the words sent.

In information theory and computer science, a code is usually considered as an algorithm which uniquely represents symbols from some source alphabet, by encoded strings, which may be in some other target alphabet. An extension of the code for representing sequences of symbols over the source alphabet is obtained by concatenating the encoded strings.

A name is a word or term used for identification. Names can identify a class or category of things, or a single thing, either uniquely, or within a given context. A personal name identifies a specific unique and identifiable individual person, and may or may not include a middle name. The name of a specific entity is sometimes called a proper name (although that term has a philosophical meaning also) and is a proper noun. Other nouns are sometimes, more loosely, called names; an older term for them, now obsolete, is "general names".

The use of personal names is not unique to humans. Dolphins also use symbolic names, as has been shown by recent research. Individual dolphins have distinctive whistles, to which they will respond even when there is no other information to clarify which dolphin is being referred to.

Caution must be exercised when translating, for there are ways that one language may prefer one type of name over another. A feudal naming habit is used sometimes in other languages: the French sometimes refer to Aristotle as "le Stagirite" from one spelling of his place of birth, and English speakers often refer to Shakespeare as "The Bard", recognizing him as a paragon writer of the language. Finally, claims to preference or authority can be refuted: the British did not refer to Louis-Napoleon as Napoleon III during his rule.