A password is a way of authentication. It can be used as a means to identify a person. Since the password is the only way to identify a person, it has to be kept secret. A password can be static. This means it will remain the same unless the user changes it, or it rarely changes. Or a password can be dynamic. A dynamic password changes regularly and does not remain the same. One type of a dynamic password is a one-time pad that can only be used once. 