SQL Server supports two security (authentication) modes:

Windows Authentication and Mixed mode

Windows Authentication mode connects to an instance of SQL Server through a Windows NT 4.0 or Windows 2000 user account.

Mixed mode (Windows Authentication and SQL Server Authentication) connect to an instance of SQL Server by using either Windows Authentication or SQL Server Authentication.

Users who connect through a Windows NT or 2000 user account can make use of trusted connections in either Windows Authentication mode or mixed mode.