The dielectric is a shield that sits directly around the conductors. The dielectric prevents multiple conductors in a cable from making contact with each other and thus prevents short circuits. In many cases, the dielectric is made of Teflon (PTFE) because of the excellent properties Teflon offers for performing this function.
Teflon does not conduct electricity, but it can become electrically charged. With a music signal that continuously changes, there is continuously a different voltage through the conductors of your cables, sometimes stronger, sometimes weaker. As a result, the charge on the dielectric also constantly changes. By externally charging the dielectric, the charge remains constant, which is better for signal transmission, lowers the noise floor and provides clearer and cleaner sound.
