Identifier

An identifier is a name that identifies (that is, labels the identity of) either a unique class of objects or a unique instance of such objects; the class or instance may be an idea, person, physical countable object (or class thereof), or physical noncountable substance (or class thereof). The abbreviation "ID" may refer to identity, identification (the process of identifying), or an identifier (that is, an instance of identification). An identifier may be a word, number, letter, symbol, or any combination of those. If the identifier follows an encoding system—wherein parts of the identifier stand for [represent] ideas or longer names—it is often referred to as a code or ID code. Identifiers that do not follow any encoding scheme are often said to be arbitrary IDs as they have no greater meaning. A unique identifier (UID) is an identifier that refers to only one instance—only one particular object in the universe. A part number is an identifier, but it is not a unique identifier—for that, a serial number would be needed, to identify each instance of the part design. For example, the identifier "Model T" identifies the class (or model) of automobiles that Ford's Model T comprises; whereas the unique identifier "Model T Serial Number 159,862" identifies one specific member of that class—that is, one particular Model T car, owned by one specific person.