A password manager is an application that stores all your passwords encrypted and fills them in for you, so you only need to remember one master password. It makes it easy to use a long, unique password for every service, and in a business it lets teams share access in a controlled way and revoke it when someone leaves.
Related term in this glossary: MFA (multi-factor authentication)
password vault, credential manager, Bitwarden, 1Password, Keeper