I think describing what I mean (or think people in general often mean) by the terms will help explain this.

The main goal is to find Product-Market fit as a first priority. This is done through prototyping, mockups, user-testing, etc, etc. Often this will be considered/called 'making an MVP'. This is an ongoing iterative process and the phase ends when you know what the core function or value proposition of the product is and who it is for.

At that point you move to the phase of building a higher quality (hopefully still very feature limited) v1.0 product.