PCB (Printed Circuit Board) is thin board that electronic components are placed, which side made from copper, this layer is conductive traces to connecting foots of electronic components.
The layer can be more than 1 side copper coated, as i know maximum are 12 layers.
PCB made from fiber or similar as non-conductive material.
The materials used in those fiber circuit boards are the fiberglass, epoxy and copper. The typical thickness of the copper on the circuit board is 35 micrometers and 17-18 micrometers.
another is known as 'paper-phenolic' or 'Pertinax' has brown colour.
It is more popular than fiberglass because the price is cheaper.
Paper Phenolic is a paper-based high pressure laminate circuit board material, has low moisture absorption and very low cold flow.
Fiberglass is absolutely only needed for plated through hole and multilayer. because fungus doesn't like it as much as paper.
Fiberglass board is also mechanically considerably stronger than pertinax, which is needed property on some applications.
PCB can be found in almost electronic device, like radio, cellular phone, TV, etc.