Database

A relational database is defined as a complex data type consisting of tables with a given amount of columns, and each column has its domain that is actually a data type (such as an integer or a date) optionally complemented by some constraints.

From SQL Server's perspective, the database is a record written in metadata and containing the name of the database, properties of the database, and names and locations of all files or folders representing storage for the database. This is the same for user databases as well as for system databases.

System databases are created automatically during SQL Server installation and are crucial for correct running of SQL Server. We know five system databases.