A Universally Unique Identifier (UUID) is a 128-bit number used to uniquely identify information in computer systems. UUIDs are designed to be unique across different systems and time, making them useful for databases, software applications, and distributed systems. They help prevent conflicts when merging data from multiple sources. UUIDs are typically represented as a string of hexadecimal digits, divided into five groups, such as 123e4567-e89b-12d3-a456-426614174000. There are several versions of UUIDs, each generated using different methods, including random numbers and timestamps. This versatility makes UUIDs a popular choice for identifying resources in various applications.