Stands for "Printed Circuit Board." A PCB is a thin board made of fiberglass or a similar material. Electrical wires are "printed" onto the board, connecting the central processor to other components on the board. Some examples of PCBs include motherboards, RAM chips, and network interface cards.
Printed circuit boards are sometimes abbreviated as "PC boards," which is fitting, since the boards are commonly used in personal computers. However, PCBs are also found in other types of electronic devices, such as radios, televisions, and computer monitors. Because PCBs are relatively flat, they can also be used in thin devices such as laptops and portable music players.