Visual thinking is an approach to understanding, communicating and  creating.  It is a collection of visualy-based concepts and methods.

The following couple of video's should give you an overview of what it's all about.

In this first TED Talks video Tom Wujec is asking an important question: how can we efficiently and effectively use our brains to understand big and complex ideas? Tom further explains how visual thinking is paramount when it comes to create, internalise and communicate ideas, information and knowledge.

In his book, "The Back of the Napkin," author Dan Roam asserts that that everyone is born with a talent for visual thinking, but that we — especially in the business world — are never encouraged to develop it. In this video, Roam shows us how anyone with a pen and a scrap of paper can exercise their imagination and work through any business problem by creating pictures.