This book is about a solution to these more intuitive problems. This solution is
to allow computers to learn from experience and understand the world in terms of a
hierarchy of concepts, with each concept defined in terms of its relation to simpler
concepts. By gathering knowledge from experience, this approach avoids the need
for human operators to formally specify all of the knowledge that the computer
needs. The hierarchy of concepts allows the computer to learn complicated concepts
by building them out of simpler ones. If we draw a graph showing how these concepts are built on top of each other, the graph is deep, with many layers. For
this reason, we call this approach to AI deep learning.