SQL (Structured Query Language) Server
Any database management system (DBMS) that uses Structured Query Language to respond to queries from client machines formatted in the SQL language, such as the Microsoft SQL Server, which is a relational database server.
The Microsoft SQL Server is a software product designed to store and retrieve data requested by other software applications. The requests could come from the same computer, or another computer on a network.
There are multiple versions of Microsoft SQL, each designed for a different audience.
Some are intended for workloads that are small single-machine applications, others for large internet-facing applications with many users, and there is many in between.