A data source is simply the source of the data.
It can be a file, a particular database on a DBMS, or even a live data feed. The data might be located on your computer, or on another computer somewhere on a network. For example, a data source might be a Microsoft SQL Server running on a Windows operating system; an IBM DB2 DBMS accessed through a gateway; a collection of Xbase files in a server directory; or a local Microsoft Access database file.
https://docs.microsoft.com/en-us/sql/odbc/reference/data-sources?view=sql-server-ver15