@password <old-password> <new-password>
Changes your player's password (as typed in the 'connect' command when you log in to the MOO) to <new-password>. For security reasons, you are required to type your current (soon to be old) password as the first argument.
Your password is stored in an encrypted form in the MOO database; in principle, not even the wizards can tell what it is, though they can change it, of course. It is recommended that your password not be your name or a common word; MOO passwords have been stolen or cracked in the past and characters have been made unhappy by such theft. Your password is your security; choose a safe one.