UUID. means Universally Unique Identifier.
The original intent while creating UUIDs was to create distributed systems to uniquely identify objects without significant central coordination. Saying which means, anyone can create UUIDs and use them to identify something. There is a very high probability the same key will never be unintentionally created by anyone else to identify some other kind of object. Objects labeled with UUIDs can therefore be later merge into a single database without needing to resolve key/identifier(ID) conflicts.
Rails 4 gives native support for the type UUID in Postgres. In the following post I will explain how we can enable and use the UUID your Rails code.