a secret word or expression used by authorized persons to prove their right to access, information, etc.

a word or other string of characters, sometimes kept secret or confidential, that must be supplied by a user in order to gain full or partial access to a multiuser computer system or its data resources.

noun

countersign , identification , key , key word , open sesame * , parole , phrase , signal , ticket , watchword , word , catch phrase , catchphrase , open sesame , password , sesame , shibboleth , slogan