Forget about prototypes the future is for Mockups
Mockup is a simplified and refined version of the user interface design that looks realistic, thought is actually a static simulation of the UI.
Taking into consideration my experience I would say that mockup is usually a full graphic composition that uses the wireframes as a template for the Photoshop.
When to speak generally about interactive mockup design, it displays a large-scale model of interactive elements that can be used for demonstration and testing of the design which looks the most realistic.
However, quite often people dismiss the meaning of prototype and mockup. The prototype is designed to display certain functional features, fully or partly. Mockup instead shows layouts of pictures, text, and buttons on the screen, and it looks similar to the real UI.
That is why people primarily use mockups which help them to have a clear understanding of the process and what's going on: where, it goes; how it looks; what colors are used for; where the text should be placed and as a result how it looks in general.