A prototype is a deliberately incomplete representation used to answer a design question before committing to the full implementation.

A low-fidelity sketch can test navigation, terminology and task sequence without spending time on visual polish. A higher-fidelity interactive prototype can test control behavior, transitions or layout more realistically.

Prototype fidelity should match the question. If the uncertainty is whether users can find an action, implementing the real database or network stack adds cost without improving that evidence.

Interaction design is iterative: propose a model, observe how representative users or evaluators interact with it, identify mismatches, revise and repeat.

Prototypes can be disposable or evolve into production code. Treating a disposable prototype as production merely because it already exists can preserve shortcuts that were acceptable only for experimentation.

Prototyping reduces the cost of discovering that the chosen interaction model is wrong by moving that discovery earlier.