Globally Unique Identifier (GUID)
A randomly generated 128-bit number that is almost certain to be unique. Used to identify a particular component, application, file, database entry, etc.
Although there is no absolute guarantee that each GUID is unique, the total number of unique keys (3.4028×1038) is so large that the probability of the same number being generated twice is very small. GUIDs are written using a four-byte word, three two-byte words, and a six-byte word. Example: