Silhouetting is when you don't think about the colours you are going to use and just focus on the shapes , forms and visual appeal of your object. The most important part part about this is to let your imagination flow and it is important to have distinctive features and shapes so they can be reconisible
This skill can also be used in planning in industry to send to 3D modelers , it is also used in everyday life on signs that you see on the street.