SQLServer is an RDBMS just like oracle DB2 from Microsoft

whereas

Structured Query Language (SQL) pronounced sequel is a language that provides an interface to relational database systems. It was developed by IBM in the 1970s for use in System R. SQL is a de facto standard as well as an ISO and ANSI standard. SQL is used to perform various operations on RDBMS

SQL - Structured Query Language - is an open vendor-independent
standardised language for accessing and manipulating data stored in
relational databases. The standards are defined by ANSI.

SQL Server is one of many products that supports and implements the SQL language.

If I write SELECT SomeField FROM SomeTable that's a SQL statement. Of course by itself simply typed into a text editor it doesn't do anything. It must be executed by a database engine that understands how to translate the SQL statement into the low-level commands required to retrieve the data from the proprietary database format. SQL Server is one such database engine.

SQL is the language

SQL Server is Application that stores the db and processes SQL