password

A word relayed to a person to gain admittance to a place or to gain access to information.

Only if a would-be visitor knew the password du jour could he pass; the guards allowed no exceptions.

A string of characters used to log in to a computer or network, to access a level in a video game, and so on; archetypally a word but nowadays often an alphanumeric string or a phrase.

A strong password has a mixture of lowercase and uppercase letters, numbers, and punctuation marks.

To protect with a password.