a material resistant to electrical conductivity that forms the platform upon which electrical components and wires can be mated (or printed) and connected to form a circuit. Usually confused with printed wiring board.

Printed Circuit Boards (PCBs) are boards, often commercially manufactured, that can represent all sorts of electrical components through the interaction of silicon layers.

PCBs were created in the early 1900's to facilitate efficient, repeatable designs for electrical connections, such as radios. Original materials and methods were difficult to make and use. After numerous inventors created and improved the process for creating these circuits, the United States opened the invention for commercial use. Eventually, the process evolved to allow mass production of these boards to reliably and efficiently create a wide variety of electrical components and systems.

From Wikipedia:

A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. When the board has only copper tracks and features, and no circuit elements such as capacitors, resistors or active devices have been manufactured into the actual substrate of the board, it is more correctly referred to as printed wiring board (PWB) or etched wiring board.

Use of the term PWB or printed wiring board although more accurate and distinct from what would be known as a true printed circuit board, has generally fallen by the wayside for many people as the distinction between circuit and wiring has become blurred. Today printed wiring (circuit) boards are used in virtually all but the simplest commercially produced electronic devices, and allow fully automated assembly processes that were not possible or practical in earlier era tag type circuit assembly processes.