UID may refer to: 1  Unique Identification Number later renamed as Aadhaar number, an initiative of Unique Identification Authority of India of the Indian government to create a unique ID for every Indian resident.2  UID = VAT identification number (in German language) (VAT: Value added tax).3  Ulster Institute for the Deaf. Unique Identification Number later renamed as Aadhaar number, an initiative of Unique Identification Authority of India of the Indian government to create a unique ID for every Indian resident. 2  UID = VAT identification number (in German language) (VAT: Value added tax). 3  Ulster Institute for the Deaf.