Energy bands are ranges of energy levels that electrons can occupy in a solid material. In solids, atoms are closely packed, and their outer electrons interact, leading to the formation of energy bands. The two main types of energy bands are the valence band, which is filled with electrons, and the conduction band, which is typically empty. The gap between these bands is called the band gap, and it determines a material's electrical conductivity. In conductors, the valence and conduction bands overlap, allowing electrons to move freely. In insulators, a large band gap prevents electron movement, while semiconductors, like silicon, have a smaller band gap that can be overcome with energy, enabling controlled conductivity.