universally unique identifier (UUID). GUIDs are 128-bit globally unique identifiers that are automatically generated based on close to two zillion frequently varying factors.

What do you think it means? It's a line from a movie. The UUID, as implemented, is neither universally unique nor exceedingly unlikely, because people keep implementing it wrong.

GUID (or UUID) is an acronym for ‘Globally Unique Identifier’ (or ‘Universally Unique Identifier’). It is a 128-bit integer number used to identify resources.