valence band

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The outermost electron shell of atoms in an insulator or semiconductor in which the electrons are too tightly bound to the atom to carry electric current.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics The highest range of electron energies in an insulator or semiconductor that can be populated; it corresponds to the valence electrons of the constituent atoms