SQL Server maintains a set of system-level databases, system databases, which are essential for the operation of a server instance.

Master:-                          The database that records all of the system level information for a SQL Server system.

Model:-                            The template for all databases that are created on the instance of SQL Server.

Msdb:-                             The database used by SQL Server Agent for scheduling alerts and jobs, and for recording operators.

                                          msdb also contains history tables such as the backup and restore history tables.

Resource(RDB):-            A read-only database that contains copies of all system objects that ship with SQL Server 2005 or later versions.

tempdb:-                           A workspace for holding temporary or intermediate result sets. This database is re-created every time an instance

                                          of SQL Server is started.When the server instance is shut down, any data in tempdb is deleted permanently.

Configure Distribution:-   A database that exists only if the server is configured as a replication Distributor. This database stores metadata

                                           and history data for all types of replication, and transactions for transactional replication.