Unlike prototypes, MVP is a functional product, not just a set of paper-based sketches.
MVP is some kind of prototype, but it takes a bit longer development process, and its technical stuffing is more complex. MVP development is necessary as a demo version of the product to test the viability of the idea.
It somehow works (not the same as poor execution, though) and already brings real value to end users. It is meant to be your ‘true’ starting point, so you can use it to start tracking purchase intent (how many users will turn into customers) or get funded.