A secret word or phrase that proves you are allowed to sign in.
Like the key to a room: it is only worth anything if it is hard to copy and you do not hand out spares.
Password Manager creates and stores a unique password for every account, and Identity Monitor watches the logins that a stolen one would produce.
How long should a password be? At least fourteen characters or a passphrase of four or more random words. Longer is better, and unique matters most.
Every WILDCARD card exists to solve one named problem. Find yours.