During the authentication process, a user asserts their identity. Once their identity is validated, the authentication provider's proof of the user's assertion is returned (usually as some sort of token). The result of this claims-based authentication system is a claims-based security token, issued by the SharePoint security token service. SharePoint Server utilizes this claims-based authentication process to provide access to resources.
When planning and configuring authentication methods, you'll need to determine which types you'll use for which web applications, which identity store will host the user identities, and the necessary supporting infrastructure for identity management.
SharePoint Server supports Windows, forms, and Security Assertion Markup Language (SAML)-based claims authentication. SharePoint also supports Kerberos-based authentication.