A wireframe is a outline sketch of layout. It doesn't look anything like the real finished product. It just shows where the various elements will be.


[![wireframe][1]][1]


  [1]: https://i.sstatic.net/QYoQ3.png


A prototype and a mock-up....there we don't have exact definitions and ways of differentiating them.

I would say that "mock-up" to me sounsd like something that is still in fairly early stages whilst a "prototype" is almost complete, a beta version almost. However this is just a feeling and generally the two words are fairly interchangable, prototype especially can be at either end of the design process.