A Request for Proposal (RFP) (or specifications) is a document prepared by a company to select a partner for the realization of a project. An RFP describes their requirements and wishes, it communicates in clear language to potential suppliers and enables them to compare and assess quotations.
Problem is, a lot of web design companies are loathe to respond to RFPs. So, you don't just pick a vendor. You're also hoping they choose you.
Discover here how to draw up a good specification.