UUID is one of those acronyms that appears constantly in computing — in your motherboard's identifiers, in software, in databases — usually without explanation. It is worth understanding, because it is a building block of hardware identity.
What a UUID is
UUID stands for Universally Unique Identifier. It is a 128-bit value, normally written as a string of hexadecimal digits in a familiar grouped form. Its entire purpose is to be an identifier that is unique not just within one program or one computer, but effectively unique everywhere, without any central authority handing them out. The closely related term GUID — Globally Unique Identifier — refers to the same idea.
How it can be "universally unique"
The obvious question: how can a value be unique everywhere if no one is coordinating it? The answer is scale and randomness. A UUID has an enormous number of possible values — so enormous that if you generate them randomly, the chance of ever producing the same one twice is, for practical purposes, negligible. Uniqueness is not guaranteed by a registry; it is achieved by making collisions so unlikely that they can be treated as impossible. Some UUIDs mix in other inputs, but the modern common approach leans on sheer randomness.
Where you meet UUIDs in hardware identity
UUIDs appear throughout the topics this site covers. The SMBIOS UUID is a UUID identifying a motherboard, set in firmware. The Windows machine GUID is a GUID — the same concept — generated at installation. Software, operating systems and databases use UUIDs constantly as identifiers for items that must not clash. When an article here mentions a "UUID" or "GUID," it is this: a 128-bit, practically-unique value used as a name for something.
Why the concept matters
Understanding UUIDs explains why certain identifiers are treated as strong. A value designed to be universally unique makes a good fingerprint component, because two different machines are extremely unlikely to share one by chance. It also explains the difference between identifiers: a UUID set in firmware is meant to be permanent and unique to that board, while a UUID generated by software can be regenerated.
The takeaway
A UUID is a 128-bit identifier designed to be unique everywhere, achieving that through sheer scale rather than a central registry. UUIDs and GUIDs are the same idea, and they appear all through hardware identity — the SMBIOS UUID, the machine GUID and more. Knowing what a UUID is makes the rest of the hardware-identity vocabulary much clearer.