What is multilayer PCB?

What is multilayer PCB?
The definition of multilayer PCB is very simple.
Multilayer PCB is a circuit board that has more than two layers.

Compare multilayer PCB with 2 layers PCB

Even though it’s a simple issue about multilayer PCB board.
But there were some guys don’t know the difference between multilayer PCB and 2 layer PCB board.
Unlike a 2 layer PCB which only has two conductive layers of material, all multilayer PCBs must have at least three layers of conductive material which are buried in the center of the material
What is multilayer PCB Stackup