Project Number Field in iProcurement

When creating a purchase requisition in iProcurement, I noticed that there is a Project field (during the Checkout: Requisition Information process). I tried testing to see if I can manually type data into that field, but it appears to require certain information. Therefore, I was thinking that this Project field is linking to a Project or Project Management module. Does anyone know for certain what this field links to and is there a way to turn off this requirement so that we can use this field as a manual entry field?

Thanks.

-Erik