Mockups are a kind of prototype that can help you introduce your idea without writing the actual application. Mockups are Proof of Concept(POC) or prototype because you would implement minimal or no functionality. Most of the time, essential scenarios are implemented in UI, design with relationships are presented, or rough visualisations of sketches can explain actual functionalities and UI. This way, it can help to save a lot of time.
Mockups are very helpful when the requirement is unclear, or UI is important. Examples are Canvas app, portal-based solutions or custom solutions. Model-driven apps do not have enough room to create mockups because navigation site map is standard. The items on forms can be arranged, but navigation would be the same. When the user interface or user experience is important, mockups can help create a better design without spending a lot of time.
The MS Visio tool can be used to create mocks and present to management or customer.
