What (briefly) is the difference between a prospectus, a proposal and a dissertation? I’m confused

Think of your prospectus as your working paper of your idea. It is your blueprint, however, it does need full committee approval and approval from Academic Review. Your proposal is Chapters 1-3 of your dissertation. Again, this needs full committee approval and approval from Academic Review. This is the fine print of your blueprint. You will orally defend your proposal. Your dissertation is the complete work (Chapters 1-5). This also needs full committee approval, approval from Academic Review, and approval from the Provost. You will orally defend your dissertation. This is the end product (it is the building your blueprint said you were going to build).