The correct answer is Length.

Passphrases are designed to be much longer than typical passwords and they emphasize length because each additional word or character dramatically increases the number of possible combinations and the effort required for brute force attacks. A long, memorable sequence of words yields high effective entropy while remaining easier for a user to recall than a short string of complex symbols.

Uniqueness is important for preventing credential reuse across accounts, but it is not the defining characteristic of a passphrase.

Complexity means mixing symbols, numbers, and varied case to meet policy rules, and passphrases generally achieve strength through length rather than forced symbol or case complexity.

Randomness can improve resistance to guessing, but many passphrases are constructed from memorable words and they rely primarily on increased length and combined entropy rather than purely random characters.

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