This is a short article to explain the fundamentals of the MoSCoW concepts. I have been using RAD (Rapid Application Development) for many years, while being a Lotus Notes developer.
Rapid Application Development does not mean lazy programming or rushed projects, but is a methodology that allows the Project Manager to cut out the "fluff" in projects and applications and to develop the right product, suited to the environment it is designed to work in.
The 80/20 Pareto Rule means that a few (20 percent) are vital and many(80 percent) are trivial. The concept of MoSCoW, it to concentrate on the vital deliverables and save the trivial to the end, or cut them all together.
Must haves - The "M" of MoSCoW, is for the priorities, the tasks that must be delivered, otherwise the project will fail. For example, if building a house, these would be the walls and roof.
Should haves - The "S" of MoSCoW, is for the secondary priorities, the tasks that need to make the product complete and without them, the product will be functional, but not as functional as it should be. For example, if building a house, these would be the plumbing, insulation, electrics, windows, flooring, fixtures and fittings.
Could haves - The "C" of MoSCoW, is for the additional tasks that would produce the best product possible. For example, if building a house, this could mean the addition of a swimming pool.
Won't haves - The "W" of MoSCoW, is for the tasks that will not be completed. If the project had all the time and money in the world, these tasks may eventually be completed, but they are superfluous to the final Product and therefore will not be delivered. For example, if building a house, this would be the Helicopter pad.
As I said, this is a very short article, but a useful one, I hope.