From ADempiere ERP Wiki
There will be many types of Proposal But I'll just some describe here About SP (Sales Proposal). It is a formal business offering from a Seller to a prospective Buyer. Your proposal will convince the Buyer that your product(s) (the thing you want to sale)and after sales service will respond to their every need (Our Product will and service will be good ). This document is essentially a sales pitch that will clearly demonstrate how, when and why you can successfully deliver products or services that will be of substantial benefit to the Buyer.