[throwawayffffas]

Entropy is really a measure of password length.

[MattPalmer1086]

That's basically right for passwords.

Of course, if we impose password complexity requirements (e.g. must have a digit or an uppercase letter), it actually reduces the entropy in the password!

[aeternum]

Entropy is a measure of the potential state space. So password length matters a lot but so does the size of the character set.