A prototype is a low or high-fidelity version of an app created to test a concept. It is a preliminary visual mock-up that looks like a real app, and that demonstrates an app's fundamental design and function, but typically does not contain functional code. A prototype can be as basic as sketches on paper or as high-fidelity as a clickable, digital model that works on your phone. It can illustrate one key screen, a complex flow, or all the main features.

A prototype is typically used in conjunction with user interviews to elicit a reaction to the app with a visual aid. A user’s reactions and responses while using the prototype will help validate if your app is on the right track.

For example, Airbnb might've made a prototype of what the process would look like to book a stay on their platform and used it in user interviews to elicit a reaction from potential users.