Gestalt is a psychology term which means "unified whole". It refers to theories of visual perception developed by German psychologists in the 1920s. These theories attempt to describe how people tend to organize visual elements into groups or unified wholes when certain principles are applied.
This ad is a good example of the Gestalt principle of similarity. Similarity is when "items are perceived as being related because they have a similar shape, color, size, etc". This uses inverse-similarity to grab and keep the viewer's attention.
this is a great example showing positive and negative space. the eye can see either a man playing a saxophone or a woman