Mock-up is the activity to  scale reproduce an object (or model).
Who realizes a mock-up is called 'mock-up artist'.

How is a mock-up made?
Depending on the project, you choose the suitable technique for the model in order to give an idea of what the customer will be realized.
For best results, remember these simple rules
• draw attention to colours and shapes
• use different sizes from original
• use different materials from the original  ones
• it doesn’t need to respect functions or use of the original object,  is only an object that resembles the original or gives a visual performance only.
Considering this facts, mock-up might quite differ from model or physical prototype.

Nowadays  the activities of  mock-up artists also turn to web design and  3d prototyping, used by engineers to design and configure complex products.