Each gray box in the PivotTable report contains the name of a field. Excel automatically puts the field names into boxes, which makes them easier to see.
As for Sum of Order Amount, because Excel summarized the numerical data in the Order Amount field by summing it up, it added a field heading that says "Sum of" the field "Order Amount."
If Sum of Order Amount isn't how you or your manager would say it, just change it—for example, "All Orders," or whatever makes sense to you. To change the name, you would select it, retype, and press ENTER.
One last thing: Sum of Order Amount is placed over Salesperson because, well, just because. When there's only one summarized data field, as in this example, Excel puts the heading for the data field over the row field heading. At least now you know where to look for it, right?