When designing a modern database or API architecture, relying on auto-incrementing integer IDs (like 1, 2, 3...) can expose your system to security risks, as hackers can easily guess user IDs (Insecure Direct Object Reference). UUIDs (Universally Unique Identifiers) solve this problem by generating a completely random 36-character string. The probability of two Version 4 UUIDs colliding is so astronomically low that it is virtually impossible.
A UUID (Universally Unique Identifier) is a 128-bit number used to uniquely identify information in computer systems. A UUID is written as a sequence of lower-case hexadecimal digits separated by hyphens (e.g., 123e4567-e89b-12d3-a456-426614174000).
GUID (Globally Unique Identifier) is simply Microsoft's implementation of the UUID standard. For all practical intents and purposes, UUID and GUID refer to the exact same thing.
A Version 4 UUID is generated using completely random numbers. It is the most commonly used version because the probability of generating a duplicate UUID (a collision) is practically zero.