A printed circuit board (PCB) is a flat board made of insulating material — typically fiberglass — with layers of copper conductors laminated onto its surfaces. The copper is etched into traces that electrically connect the components mounted on the board. Electronic components such as chips, resistors, and capacitors are soldered to pads on the board, which both electrically connects and mechanically fastens them. PCBs are the structural and electrical backbone of virtually all modern electronic devices.
Development boards like the [Seeed Studios](A10-Glossary/Seeed Studios.md) XIAO series are small, ready-made PCBs that expose a microcontroller’s pins in a breadboard-friendly form factor, making it easy to prototype and build custom devices without designing a board from scratch.