Multilayer PCBs are circuit boards with four or more layers, separated by insulating dielectric layers and connected by conductive vias. This construction allows for higher circuit density, improved electromagnetic shielding, and reduced signal interference. They are used in demanding applications such as telecommunications, automotive, and medical technology, where reliable and compact electronic solutions are required. By combining multiple signal, power, and ground layers, multilayer PCBs provide high performance and design flexibility for modern electronic systems.