What is the difference between PCB and motherboard?
The abbreviation of PCB is a Printed Circuit Board, PCB is just a thin piece of board that allows electronics component to be connected to each other. It uses conductive pathway to track, or to signal trace etched from copper sheets laminated on to a non-conductive substrate. The circuit wire are clearly built on the board. The PCB can also referred to as printed wiring board or etched wiring board.
As clearly the answer to this question is: A printed circuit is just a printed wiring board,is just a piece of board, it is pure; there are no electronic component are placed on the board yet. 
A mother board is a board which all electronics component are built on the printed circuit board already, as a main board of a microcomputer. Motherboard is generally rectangular circuit board, the main circuit of the computer system was installed above, generally have the BIOS chip, I/O control chip, key and the panel control switch interface, lamp plug pieces, expansion slot, and the main board and card of dc power supply connectors and other components.