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.
Modern passwords are made of characters, letters and numbers. Sometimes a password will require a minimum number of characters. Usually this is from six to eight. Some websites allow only the use of letters and numbers, but no other characters on the keyboard. Other websites advise using a combination of letters and numbers to increase the "strength" of a password. Websites also advise changing a password once a year or more often to prevent hacking. A person may be able to guess a password if it is too easy. While being typed, each letter of a password is shown as * or •.