MSSQL usually refers to Microsoft SQL Server, a relational database platform used to store and query business data. In security work, it is important because a database server is not always just a data store: if it is exposed, poorly configured, or compromised, it can become a pivot point into the wider environment. Features such as extended procedures, linked servers, SQL Agent jobs, or command-execution options like xp_cmdshell can expand what an attacker can do from a database foothold.
Attackers target MSSQL for database theft, credential hunting, code execution, and lateral movement. Defenders reduce risk by limiting network exposure, enforcing strong authentication, disabling risky features unless needed, patching promptly, and monitoring for unusual queries, privilege changes, and OS-level command activity from SQL Server processes. In practice, MSSQL security is part database security, part host security, and part identity protection.