Aadhaar is a 12-digit unique identification number issued by the Indian government to every individual resident of India based on their biometric and demographic data. When you apply for Aadhaar, you have to visit an Enrolment Centre and fill the enrolment form. After giving demographic and biometric data and submission of proof of Identity and address documents you get an acknowledgement slip which has your Aadhaar Enrolment ID or Aadhaar Enrolment number.
The Unique Identification Authority of India (UDAI), which functions under the Planning Commission of India, is responsible for managing Aadhaar numbers and Aadhaar identification cards.
