To revise means to alter or improve a preliminary draft of something, usually a text. When you want your writing to be really great, you must revise it several times until it is perfect.
The word revise sounds like the related word revisit, and revising a piece of work does in fact require revisiting it. Planning out a project includes estimating how much it will cost and when it will be done. If something unforeseen happens, you might have to revise your estimates of cost and completion date. You can also use revise as a noun. Once you finish the first draft of an essay, you can begin working on the revise.