"A request for proposal (RFP) is a business document that announces a project, describes it, and solicits bids from qualified contractors to complete it."

Basically, it's a long laundry list of requirements for things you want to buy (e.g. software), with some vague justification attached. It's a thing in big companies and public institutions, which are supposed to have a high degree of oversight on any move they make. In practice, it's just another source of Bullshit Jobs, since the company publishing an RFP has likely already decided what they are going to buy and just have to go through the motions - a bit like those companies publishing job ads because they have to, when they already know who they are going to hire.