WordNet (r) 3.0 (2006):

identifier
    n 1: a symbol that establishes the identity of the one bearing
         it

The Free On-line Dictionary of Computing (30 December 2018):

identifier

   1.  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.

   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.

   (2006-05-29)

   2.  (id) A primary key.  The column containing a
   table's primary key is frequently named after the table with
   "_id" appended, e.g. "customer_id".

   (2006-05-29)