OpenID Connect (OIDC) is an authentication layer built on top of OAuth 2.0 that allows users to authenticate once and gain access to multiple apps without re-authenticating. It's commonly used for Single Sign-On (SSO), which helps websites and applications verify the identity of users without needing to manage and store sensitive details like passwords. The main advantages of OpenID Connect are standardization, ease of implementation, security, and broad support across different types of clients and identity providers. OIDC works by extending OAuth 2.0 with an ID token that contains user authentication information. It supports various flows for different types of apps, such as Authorization Code flow, PKCE flow, Implicit flow, and Hybrid flow. Best practices include using secure connections, validating ID tokens, handling redirect URIs securely, and implementing appropriate OAuth scopes.