Difference between Waterfall and Unified Process

The main difference between the Waterfall model and the Unified Process is that the Waterfall model proceeds from one phase to the next in a purely sequential manner, while the Unified Process’ phases are divided into a series of timeboxed iterations.

Are we able to go back one step in the Waterfall model?

No, the Waterfall model strongly recommends that one should move to another phase only when it’s current phase is completed and perfected. It also states that phases of development in the waterfall model are discrete, and there is no jumping back and forth or overlap between them

Why are there many spirals in the Spiral Model and What is the benefit of it.

The reason to why there are many spirals in the Spiral Model is so that the project team is able to take advantage of the development process as they work best when they are both incremental in repetitive. The benefit of the spirals in the Spiral Model is that the project team is able to start small and benefit from trial and error steps along the way.

What do you mean the Unified Process is "iterative" and What is an "iterative" in the Unified Process?

It means that the Unified Process is repetitive. The Unified Process is based on repetitions, where each repetitive result in an increment, which is a release of the system that contains added or improved functionality

In the Spiral model, what is "rapid prototyping"?

Rapid Prototyping is the creation of a working model of the software to demonstrate the feasibility of the function before the release of the final end product.