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1640s, "regard as the same," from French identifier, from identité (see identity). Sense of "recognize" first recorded 1769. Meaning "make one (with), associate (oneself)" is from 1780. Sense of "serve as means of identification" is attested by 1886. Related: Identified; identifying.
Each different type of entity may have a different range of valid identifiers or "name space". For example, an identifier in C is a series of one or more letters, digits and underscores that does not begin with a digit. An identifier has a type, e.g. integer variable, hash, variant and a scope, e.g. block, global.