Definitions
1.nounSomeone who identifies; a person who establishes the identity of.
2.nounSomething that identifies or uniquely points to something or someone else.
3.nounA guidebook that helps determine the specific class of an object (such as a mushroom, herb, fish, bird, drug, or mineral), or its individual identity (such as that of a star).
4.noun(operating systems) A formal name used in source code to refer to a variable, function, procedure, package, etc. or in an operating system to refer to a process, user, group, etc.
5.nounA code that distinguishes a particular element from all other elements in a document.
6.nounA primary key.