It is Database Management System.
Database : Database is a well structured format to store data like Files, Tables, Excel sheets etc.
Database Management System : It is a package of software which control the creation, maintenance, and the use of a Database. It allows organizations to conveniently develop databases for various applications by Database administrators (DBAs) and other specialists. A database is an integrated collection of data records, files, and other database objects. A DBMS allows different user application programs to concurrently access the same database. DBMSs may use a variety of database models such as relational model or object model.