A Vendor in the POR App is any entity from whom you purchase goods and/or services. It can be raw material suppliers, contractors, consultants, office supplies providers etc.
Once a new vendor is added to the POR App, you can select the vendor from a saved list while creating subsequent PORs related to that vendor.
If the bank account details of a vendor is present, you will be able to issue payouts to them from within the POR App via the RazorpayX integration. (You will need to have an active RazorpayX account for the Payout functionality.)