Something that identifies or uniquely points to something or someone else.
A 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).
(programming, 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.
The Identifier personally inspects each horse in each race by verifying the lip tattoo, body color, head and leg markings, scars, and chestnut (night eyes).
The foal papers are documents recording the horse's registration; no horse can start in any race unless his papers are in the hands of the track's identifier.
Prehistoric artists used hand-prints in cave paintings, perhaps as as 'signature'. They might be considered the earliest example of a biometric identifier.