A prototype is a clickable simulation of a product – connected screens you can move through like a real application – used for user testing before programming begins.
A prototype answers the process's most expensive question – "will this work for people?" – before the answer starts costing months of development. Testing a prototype with five users uncovers most critical problems at a fraction of the cost of fixing them in code.
Prototypes vary in fidelity: from linked wireframes (testing structure and flow) to pixel-perfect simulations with animations (testing interaction clarity, investor demos).
The limit: a prototype pretends to have logic but has none – it won't verify performance, real data or integrations. That is what an MVP is for.