The Data Source is the final result of all the actions (Join, Union, Split, Pivot, and more) when connecting to a dataset, and all the customization you can apply afterward (Hide, Rename, Add Aliases, and so on). The goal for your Data Source is to be as performant, simple, and easy to understand as possible.

A Data Source can be a Live connection , an Extract , or published on Tableau Server . But no matter the type of connection, you will always find the same elements.