what is a Waterfall model in system devolpment respectivly compair
with other any two models.

bl**dy students!  Just go to the class!

What does your text book say?

Waterfall is based on the fact, the the software gets only one
iteration thru the loop. Planning->development-> testing-> deployment.
so all the bugs that are discovered on the testing phase, get
documented, but not fixed.

The other two, redo the development or even the planning stage
severalt times, depending on the testing results.

You can see the pros like speed and aso the cons like bugs. When you
have a really qualified coding force, you can pump out software fairly
quickly.