Prototype

A prototype is a clickable, testable version of a design, real enough to interact with but not actually built. It lets you put a functional representation of your site in front of real people and watch what they do before a single line of code is written.

The point is to learn cheaply. A prototype might be rough wireframes linked together or a polished mockup that feels nearly live. Either way, it turns abstract design decisions into something you can run through usability testing, catching confusion while it is still easy to fix.