1. Algorithm Difference: OTP (One-Time Password) is a one-time use code generated based on a mathematical algorithm but TOTP (Time-based One-Time Password) is generated using a time-based algorithm which changes after a specific time interval.
2. Time Dependency: OTPs are not time-dependent and can be used at any time within their validity period, whereas TOTPs are bound by time and are only valid for a short duration before expiring.
3. Offline Usage: OTPs can be generated and used offline without any need for synchronization, whereas TOTPs require synchronization between the device generating the password and the service validating it.
4. Synchronization: OTPs do not require synchronization between the client and the server, making them simpler to implement, while TOTPs need synchronization to ensure that the password generated by the client matches the one expected by the server.
5. Replay Attack Mitigation: TOTPs are designed to mitigate replay attacks by constantly changing the generated password based on the current time, providing an extra layer of security compared to OTPs.
6. User Experience: In terms of user experience, TOTPs are more user-friendly as they automatically change at set intervals, reducing the risk of human error in generating or inputting the password compared to OTPs.

In Summary, the key differences between OTP and TOTP lie in their algorithms, time dependency, offline usage, synchronization requirements, replay attack mitigation, and user experience.