Jack ( /ˈdʒæk/) is a male given name, although in very rare cases it can be used as a female given name, and sometimes as a surname. In English it is traditionally used as the diminutive form of the name John or the first name Jackson, though it is also often given as a proper name in its own right.
The name Jack is unique in the English language for the frequency of its use as a verb and a noun for many common objects and actions; and also its use in many compound words and phrases: jackknife, jackpot, jack tar, hijack, union jack, jack straw (scarecrow), apple jack, lumberjack, jackhammer, jackdaw, jack o'lantern, jack-in-the-box, jack of clubs (playing cards), etc. The Encyclopædia Britannica article on the history of the word "jack" linked it directly to the common name: "Jack, a word with a great variety of meanings and applications, all traceable to the common use of the word as a by-name of a man."
The name Jack probably originated as a medieval diminutive of the name John, originally as "Jackin" (earlier Jankin). Alternatively it may be derived from the name Jacques, which is the French form of the name Jacob. There is also a theory that it is Celtic in origin, meaning "Healthy, Strong, Full of Vital Energy" (compare the Welsh word iach, "health"), from a putative Ancient British *Jakkios. Whatever its origin, the name and also the word "jack" were long used as a term to refer to any man, especially of the common classes.
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.