I agree with Mr. Nilesh Soni, and UAN means Universal Account Number.
Understanding UAN (Universal Account Number)
UAN stands for Universal Account Number. The UAN will act as an umbrella for the multiple Member IDs allotted to an individual by different establishments. The idea is to link multiple Member Identification Numbers (Member ID) allotted to a single member under a single Universal Account Number. This will help the member to view details of all the Member Identification Numbers (Member ID) linked to it. If a member is already allotted a Universal Account Number (UAN), then he/she is required to provide the same on joining a new establishment to enable the employer to, in turn, mark the newly allotted Member Identification Number (Member ID) to the already allotted Universal Identification Number (UAN).
Purpose of Introducing UAN
The basic idea of introducing UAN is to avoid PF withdrawal by the members when they move from one organization to another organization and to avoid difficulty in transferring their PF account. As most of the members are opting for PF withdrawal once they leave an organization, even though they are getting a job before 2 months (by declaring they don't have a job after 2 months also), which is unethical and there is no control over that. So by introducing this UAN, most of the problems will be rectified, and only those who are really eligible (not got a job within 2 months) can opt for PF withdrawal. After withdrawing PF, if they get any new job and PF is applicable in the new organization, with the same UAN, they can start their new PF account in the new organization. So UAN is a lifetime number irrespective of the number of organizations in your career henceforth. This is as per my knowledge. Correct me, seniors, if I am wrong.