In this field you can enter the requested (desired) delivery period. The requested delivery period is then used internally to compare the actual delivery period with the requested delivery period in the Supplier Rating procedure.
If you have activated the setting Automatically Update Requested Delivery Period on Orders/Inquiries?, under the section Orders / Inquiries under the Purchase tab in the Settings procedure, this field will always be automatically updated to the Delivery period on a new order row until that row is saved. However, you have the option of changing the requested delivery period afterwards. See the setting Question when changing Current period, applies to frozen Initial/Requested period under the abovementioned tab.