conduction band

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

• noun The set of electron orbitals, generally the outermost shells of the atoms in a conductor or semiconductor, in which electrons are free to move and thereby carry an electric current.

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

• noun physics The range of electron energies in an insulator or semiconductor in which electrons can move freely and transport charge.