UUID

Universally Unique Identifier

128-bit ID effectively guaranteed unique without coordination.

When you'd see it: Software and database design, whenever a system needs IDs that will not collide across machines or systems.

Why it matters: A UUID is a 128-bit identifier random enough to be treated as unique without any central coordination, so independent systems generate IDs that never clash. The tradeoff is that they are long and not human-friendly.