Mockup Vs Prototype. As such the prototype will not be fully functional but elements will be interactive enough for core concepts to be validated. You might want to try marvel invision or moqups.
You can test it present it to clients for approval etc. To some extent a prototype is a fully interactive functional mockup with high fidelity uis rich interactions and animations. Insightful discussion on quora about the difference between wireframe mockup and prototype here another discussion on the same topic here.
One picture is more than a thousand words.
A prototype is an almost complete clickable and functional product. The mockup shows how exactly the application is going to look. Mockups are particularly useful if you want to get early buy in from a stakeholder. Unlike a wireframe a mockup looks more like a finished product or prototype but it is not interactive and not clickable.
