[enraged_camel]

Agile is the idea that requirements are always in flux, and therefore it's pointless to spend time upfront gathering requirements and writing specs and following those specs since there's a good chance they will have become irrelevant by the time the product ships. So agile says "just get something, anything, out the door as soon as possible, receive feedback, then keep revising."

Waterfall is the opposite approach, where you have a formal requirements gathering phase, then you commit everything into design docs, and follow those docs with as few changes as possible. It's similar to how a house is built: first you check your local zoning laws, then have an architect draw the plans, then dig a hole and build a foundation, then build the skeleton, the walls, etc. You don't tell the client, "hey, we just dug the hole for the foundation, come live in it for a few weeks and give us feedback so we know what part to build next."