Paid By contains system default Pay Type 'Paid By' Methods.
The paid by methods are options available within 'Pay Types' to choose how the Payees are 'paid by'.
Per Day - Paid by a per day rate
Per Hour - Paid by a per hour rate
Per Kilometre - Paid by a per kilometre rate
Per Lump Sum - Paid by a per lump sum rate
Per Pay Period - Paid by a per paid period rate
Per Piece - Paid by a per piece rate
The Paid By Methods are included by default and are not able to be edited. However, if you wish to add a user modified Paid By Method, you can refer to How do I add a new Paid By Option?