"A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets laminated onto a non-conductive substrate. Alternative names are printed wiring board (PWB),and etched wiring board." from Wikipedia - Printed Circuit Board. In its more pure form it is simply a normally flat plastic or ceramic substrate in which alternative layers of insulators and conductors are grown sequentially to form isolated conductive paths to transfer signals and current in and out of electronic components.

PCB (printed circuit board) layout optimization to avoid EMI (electromagnetic interference). A PCB layout should not only strive to prevent the emission of noise but also have good noise immunity from outside sources. One should have an understanding of potential sources of noise and have a strategy for dealing with these problems.