The document discusses electrical conductivity in materials. It explains that conductors allow electricity to flow through due to free electrons in their outer orbital shells. Insulators do not allow electricity to flow because there is a large forbidden energy gap between their valence and conduction bands, preventing electron movement. Semiconductors have properties between conductors and insulators, with a small forbidden gap that allows some electron movement when certain conditions are met. Electrical conductivity depends on the electronic structure and availability of free electrons in the material.