Single Sign On (SSO) is an authentication mechanism that means the same set of credentials can be used by a user on multiple applications without requiring them to create a new account each time they log in.
Social Login is also known as social sign-in or social sign-on. It uses information from social networking sites to help login into a third-party application or website. This eases the sign-in and registration process as there is no mandate on new account creation.
You can learn more about SSO and social login in this infographic by LoginRadius.