globally unique identifier (GUID - Global Unique Identifier), GUID is a 128-bit globally unique identifier (GUID - Global Unique Identifier), GUID is a 128-bit binary number (16 bytes) that can be used for GUID is a 128-bit globally unique identifier (GUID - globally unique identifier), GUID is a 128-bit binary number (16 bytes) that can be used on all computers and networks that require a unique identifier. The likelihood of duplication of this identifier is very low. The format of the GUID is "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx", where each x is a hexadecimal number in the range 0-9 or a-f.