…a working prototype. Iterations must become subtractive. Designer’s focus needs to become narrower. Everything that has no significant purpose and does not solve the user’s needs, has to be either removed or redesigned in a way that it will be available when it’s needed.
Keeping your idea malleable and changing for as long as possible is, in my experience, much more healthy and leads to far better end-results. Ideas should be subjected to a healthy dose of darwinism before being pursued. Survival of the fittest. You want to evolve the best version of your idea, and to that end, it can make sense to talk about a circular process within this phase.