System database : An Overview

Master

It records all the system-level information for an instance of SQL Server.

Msdb

It is used by the SQL SERVER Agent for scheduling the alert and jobs.

Model

It is used as the template for all databases created on the instance of SQL Server.

Modifications made to the model database, such as database size, collation, recovery model, and other database options, are applied to any databases created afterward.

Resource

Is a read-only database that contains system objects that are included with SQL Server.

System objects are physically persisted in the Resource database, but they logically appear in the sys schema of every database.

Tempdb

Is a workspace for holding temporary objects or intermediate result sets.