Wikipedia definition:

In physics, chemistry, and electronic engineering, an electron hole is the lack of an electron at a position where one could exist in an atom or atomic lattice. It is different from the positron, which is an actual particle of antimatter. (See also Dirac Sea.) If an electron is excited into a higher state it leaves a hole in its old state. This meaning is used in Auger electron spectroscopy (and other x-ray techniques), in computational chemistry, and to explain the low electron-electron scattering-rate in crystals (metals, semiconductors). In crystals, electronic band structure calculations lead to an effective mass for the electrons, which typically is negative at the top of a band. The negative mass is an unintuitive concept, and in these situations a more familiar picture is found by considering a positive charge with a positive mass.

Source: Wikipedia - Electron hole