Globally Unique IDentifier
special group of identifiers : 128-bit values that are statistically guaranteed to be unique across time and space.
You can generate a GUID through the MS command line utility UUIDGEN.EXE, or by a MS sample VC++ dialog application called GUIDGEN.EXE.
GUIDs are 128 bits numbers, where the first 60 are time-dependent, and the last 48 are machine-dependent (they depends by the machine under which you generate it).
example of GUID (using UUIDGEN.EXE):
"
C:\>UUIDGEN.EXE <CR >
01b0b8d0-f2bd-11d4-89c7-00a024ac3a23
"
This is a world-wide unique ID , because it was generated on my PC, with its HW properties, and on that particular time (12:26:39 A.M. of the 25th of January 2001).