How do we find what we are looking for? And how do we do it?
Visual search deals with the problem of how we find what we are looking for (relevant things) in a world full of things that might also be irrelevant to us.
Visual search is necessary for our daily life. Imagine we have to process all the information in our visual field at once. It is simply not possible because of our limited cognitive capacity. Visual search is also very important for design.
See this example: