Term:guid [Globally Unique IDentifier]
GUID (typically pronounced “gwid”) is an acronym for Globally Unique IDentifier.
A GUID is nothing more than a 128-bit number, though it’s often displayed as a sequence of 32 hexadecimal digits with dash separators and enclosed in curly braces. Example:
A 128-bit number has 340,282,366,920,938,463,463,374,607,431,768,211,456 possible values.
GUIDs are generated using algorithms to ensure sufficient randomness and diversity that the “unique” portion of the name is as true as possible. When generated properly, it is statistically nearly impossible that two GUIDs will be created with the same value. (Unfortunately, less-than-proper techniques, including simply copying existing values, are in occasional use.)
GUIDs are used to identify many different things, and are most frequently used when uniqueness of identification is important, difficult, or inconvenient to ensure by other means.
When generated according to the standard methods, UUIDs are, for practical purposes, unique. Their uniqueness does not depend 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.
Thus, anyone can create a UUID and use it to identify something with near certainty that the identifier does not duplicate one that has already been, or will be, created to identify something else. Information labeled with UUIDs by independent parties can therefore be later combined into a single database or transmitted on the same channel, with a negligible probability of duplication.
Adoption of UUIDs is widespread, with many computing platforms providing support for generating them and for parsing their textual representation.