Short version: A clickable or testable model that shows how a design should work before development.
In creative work, prototype shapes how an idea becomes something people can see, read, use, or remember. It can guide layout, hierarchy, visuals, copy, interaction, production, or the overall feeling of the output. The decision should serve the message, the brand, and the situation where the work will actually appear.
The point is not decoration for its own sake. Good creative choices make the message easier to understand and the brand easier to recognize, while still fitting the channel and the audience’s real behavior. When creative work is judged only by taste, teams can miss whether it is doing its job.