An Identity Provider, often referred to by the acronym IdP, assumes a role similar to that of a virtual guardian.
Its main function is to store and administer the data needed to authenticate the identity of users when they access websites or online applications. The best-known Identity Provider (IdP) is Microsoft Entra ID (formerly Azure Active Directory).
If you'd like to find out more about setting up SSO, read this article: How do I set up SSO?