An OPT, or One-Time Password, is a security feature that generates a unique password for each login attempt or transaction. Unlike traditional passwords, which remain the same until changed, an OTP is valid for a single use and expires after a short period. It is often delivered to the user through email, SMS, or an authentication app, providing an extra layer of security by ensuring that even if a password is compromised, unauthorized access is still prevented. OTPs are commonly used for two-factor authentication (2FA) to protect online accounts and sensitive data.