Global (Universally) Unique Identifier
A universally unique identifier (UUID) is a 128-bit number used to identify information in computer systems. The term globally unique identifier (GUID) is also used.
When generated according to the standard methods, UUIDs are for practical purposes unique, without depending for their uniqueness on a central registration authority or coordination between the parties generating them, unlike most other numbering schemes. While the probability that a UUID will be duplicated is not zero, it is close enough to zero to be negligible.