Two
Factor Authentication. Or Three Factor Authentication. (You see, there's
ambiguity in the definition of this
TLA)
In most situation, you only need a single
factor to authenticate, to prove who you are: "Something you know" - typically a password. But that's not very secure. Therefore, some systems make authentication stronger by requiring more than just one factor. Other factors are "something you are" (such as your fingerprint, or other biometric aspects such as your signature) and "something you have" (such as a key, or a chipcard).
Every
ATM I have seen so far employs TFA: In order to get money out of it, you have to prove that you're the legitimate account
holder by providing two things: Something you have (your
ATM card) and something you know (your PIN).