Microsoft SQLServer (MSSQL) is a software application that is a relational database management system. It's mainly used as database software to store and retrieve data. This is built on top of SQL, that is, Structured Query Language: http://searchsqlserver.techtarget.com/definition/SQL.
The current release, that is, SQL Server 2017, is more robust and can be used on Windows and Linux. You can get SQL Server 2017 from here: https://www.microsoft.com/en-IN/sql-server/sql-server-2017. Please note that we will use SQL Server 2008 R2 or later in this book.