What is an MVP in software development?

The version that works is the smallest thing that completes one real loop end to end for one type of user — they arrive, do the thing, and get the value. It is not a subset of every planned feature half-built. And it needs enough instrumentation to tell you whether people are completing that loop, because an MVP that ships without measurement gives you opinions instead of evidence.

The decision to make consciously is what happens to the code afterwards. A throwaway prototype can cut corners freely; a first version you intend to keep building on cannot, and pretending otherwise is how a product ends up rewritten in its second year. Neither is wrong, but they justify different levels of care, and it is much cheaper to choose deliberately than to discover which one you built.