globally unique identifier (GUID-globally unique identifier), GUID is a 128-bit globally unique identifier (GUID-globally unique identifier), GUID is a 128-bit binary number (16 bytes) , available for all computers and networks that require unique identifiers. It is very unlikely that this identifier will be repeated. GUIDs are in the format "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx", where each x is a hexadecimal number in the range 0-9 or a-f.