It is an one-time temporary password (OTP), that is generated by an algorithm and valid only for 30 seconds. Because of this time variable characteristic, it is called TOTP. TOTP is 8 digit long numeric string. TOTP is personal to the resident and is uniquely generated every 30 seconds for each resident separately. With time-based OTP, the TOTP validation server and token generation app(like mAadhaar) use their respective system times to generate OTPs. The TOTP algorithm assumes that the system times are synchronized.
Aadhaar a UIDAI project to issue a unique Aadhaar 12 digit number to every citizen of India printed on their respective Aadhaar Card. A noob person can easily get familier with all the process about Aadhaar Card in this blog, every answers which you are searching related to Aadhaar Card you will find it here.