Aadhaar is a unique 12-digit identification number issued by the Unique Identification Authority of India (UIDAI) to any individual residing in India. It is obtained by submitting valid proof of identity and address documents during enrollment, providing biometrics, and receiving an enrollment number. Aadhaar helps to establish a person's identity and is useful for functions like opening bank accounts, receiving government subsidies, and education. However, the enrollment process can be time-consuming and there is a risk of corruption, as the system is not fool-proof. Aadhaar is also not meant to determine citizenship.