Sadr highlights returning or going away, while wadaʿ highlights bidding farewell. Both terms designate the same tawaf near the end of the Hajj journey.
For instance, a non-Makkan pilgrim makes one seven-circuit farewell tawaf before departing. Calling it either Tawaf al-Sadr or Tawaf al-Wadaʿ does not create another set of seven circuits.