Many apps today ask for a code after you enter your password. Sometimes this is called OTP, and sometimes Two-Factor Authentication. They are related, but they are not the same thing.
Two-Factor Authentication (2FA) is a security system. It protects an account by requiring two different kinds of proof before allowing access. These proofs usually come from two categories: something you know (like a password), something you have (like your phone), or something you are (such as a fingerprint or face scan). The idea is simple. Even if someone steals your password, they still cannot log in without the second layer.
An OTP, or One-Time Password, is a temporary code sent to your phone, email, or authentication app. It works only once and usually expires within a few minutes. An OTP is not a security system by itself. It is just one way to provide the second proof required in Two-Factor Authentication.
Think of it like entering a building. Your password is the main key. Two-Factor Authentication adds a security guard who asks for extra verification. The OTP is the passcode you show the guard.
Not all OTP use means full 2FA. Some services send OTPs only for login convenience or verification, not as a true second factor. Meanwhile, 2FA can also work without OTPs, using biometrics or security apps instead.
Two-Factor Authentication is the broader protection method, while an OTP is one of the tools used to make that protection work.