Stands for "Globally Unique Identifier." A GUID is a 128-bit (16 byte) number used by software programs to uniquely identify the location of a data object. Some examples of data that include GUIDs are streaming media files, Windows registry entries, database keys, and various file types. GUIDs are typically written in hexadecimal notation, containing 32 digits, and may look something like this:
Globally unique identifiers are also the basis of the GUID Partition Table (GPT). This is a hard disk partitioning scheme proposed by Intel as part of the Extensible Firmware Interface. It is used by Windows PCs as well as Intel-based Macintosh computers. GPT uses GUIDs to define the different partitions on a hard drive. Some examples include the boot partition, the file system partition, and the data partition. Each operating system that supports the GPT partitioning scheme uses specific GUIDs to label each partition.