key
A coded string used to relate objects with corresponding objects in a database.
A key is any identification number, alphanumeric string, or similar specifier used as a primary key or object identifier. Keys are used to represent unique objects in a database, and to identify commonalities between objects in different databases.
The number or string identifies an object within the system that assigns it. Its meaning therefore depends on that system; identical characters in unrelated registers need not identify the same subject.
A record can retain an internal identifier and references to corresponding objects in external databases. These keys provide different system-specific references to the subject, without requiring that their values or formats be identical.