Printed circuit boards brief:

A Multilayer PCBs consist of multiple layers of electronic components placed over each other.

Through-hole construction was the technology that was used to deal with planting the electrical components through the holes on the Printed Board Curcuit and then soldering them together. When this technology was found wanting in complex cases, Point-to-Point construction technology evolved. This proved to be better than its predecessor, but in no way is it comparable to a multilayer PCB. The development of multilayer PCB has  allowed electronic companies to drastically cut down on the cost and size of their products.