What is the difference between SSO and Social sign-on in salesforce?

Social sign-on
Social login is a form of single sign-on using existing information from a social networking service such as Facebook, Twitter or Google+, to sign into a third party website instead of creating a new login account specifically for that website.
Single sign-on
Single sign-on (SSO) is a session and user authentication service that permits a user to use one set of login credentials (e.g., name and password) to access multiple applications. SSO can be used by enterprises, smaller organizations, and individuals to mitigate the management of various usernames and passwords.