A time-based one-time password (TOTP) is a temporary passcode, generated by an algorithm, for use in authenticating access to computer systems. The algorithm that generates each password uses the current time of day as one of its factors, ensuring that each password is unique. TOTPs are commonly used for two-factor authentication (2FA). In 2FA scenarios, a user must enter a traditional, static password and a TOTP to gain access.
Nexus Personal Mobile offers extra security compared to other mobile apps for two-factor authentication, since you also authenticate yourself in Personal Mobile with a PIN code or your fingerprint before you receive the OTP. Read more here: Compare Personal Mobile with other mobile OTP apps.