In your code behind, you would bind a DataSet or some other object to a control on your form. In your markup, the statement you gave then uses whatever object you bound to your control to look up the value with a key of Prod_Id.

So, if you bound a DataSet to a ListView and had a template set up for your listview, your statement would show the value in the Prod_Id column as the text for whatever element the statement is used in.