Minimum Viable Prototype is a simulation of your design to test the product/service with your target customer. Unlike MVP it is not a product that could be sold but a simulation of a product functionality using sketches, maquettes, walkthroughs and other methods.
Prototyping and Testing stages of the Design Thinking are two intertwined processes with a lot of feedback loops. You build your minimum viable prototype, test it, analyze the results (define stage) and make the conclusions on how to improve your solution (ideate stage). Then, you build a new prototype, test it again and repeat this process until you are satisfied with the end result.
You may think that prototypes unnecessarily take time and are a waste of resources. But in fact, they allow you to save a lot of money and avoid creating a product that no one is going to use. Prototypes are built to fail fast and cheap in the early stage, to avoid costly failures and reputation damage in the latter stages.