Most people, including most electrical engineers, think of electricity as electrons flowing in a wire, much like water flowing in a hose. The idea of electrical energy moving through free space in a wave is a completely foreign concept. Yet, electromagnetic radiation is exactly that, electrical energy moving through space as a wave, and electrical energy in a wire is a special case in which the energy is guided by a wire. Some of the energy is internal to the wire, and some of the energy is external to the wire. When we plug an appliance into the receptacle, the power delivered to the appliance does not actually "go through the cord", but is electromagnetic energy being "guided" by the electron activity in the power cord. The electromagnetic energy delivered to the load is external to the wire. The electron activity oscillating back and forth in the wire is a result of the external electromagnetic energy and in turn serves as a way of telling the electromagnetic wave to follow the wire. The electron movement in the wire is proportional to the strength of the wave being guided. Don't be disturbed if you have difficulty grasping this concept. Even engineering students have difficulty understanding it.