Answer : 2. "One Time Password"
Explanation :

1. The full form of OTP is One one-time password.

2. OTP is used as one of the additional security features for secure online transactions.

3. The OTP feature prevents certain types of identity theft by ensuring that a captured username/password pair cannot be used a second time.

4. The user's login name usually remains the same, and the one-time password changes with each login.

5. One-Time Password (aka One-Time Passcode) is a form of strong authentication, providing better security to eBanking, corporate networks, and other sensitive data systems.