Noun
English Wikipedia has an article on:Fermi surfaceWikipedia
Fermi surface (plural Fermi surfaces)
(physics) An abstract boundary, of constant energy, useful for predicting the thermal, electrical, magnetic, and optical properties of metals, semimetals, and doped semiconductors.
Because the technique is sensitive to the angle of the emitted electrons one can determine the spectrum for different wave vectors on the Fermi surface. Source: Internet