When you get an Aadhaar card, you also give the government your fingerprint and retinal scan data. This is called biometric data. Your biometric data can be used for Aadhaar verification. When you submit an Aadhaar card as a proof of identity to get a SIM card, you can use your fingerprint to allow the telecom company to access your identity information. By doing this, it can quickly authenticate the ID, speeding up things like KYC verification.