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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).
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).
by Securitoot January 15, 2013
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