The UID number is a unique identifier that's assigned to everyone who enters the UAE. When you first apply for residency, the General Directory of Residency and Foreign Affairs (GDRFA) and the Federal Authority for Identity and Citizenship (ICP) will give you one automatically. This number links a person's information from different government databases, like residency,
visa, and immigration records.
This number doesn't change while you're in the UAE, even if your visa gets cancelled or you change it.