An Identity Provider (IdP) is a service that manages user identities and provides authentication for applications. It verifies users' credentials, such as usernames and passwords, and issues tokens that allow access to various services without needing to log in multiple times. This simplifies the user experience and enhances security. IdPs are commonly used in systems that implement Single Sign-On (SSO), allowing users to access multiple applications with one set of credentials. Popular examples of IdPs include Google, Microsoft, and Okta, which help organizations manage user access and streamline the login process across different platforms.