1. The release of electrons from a specific material into the surrounding area or space.

It may be caused by an electric field, light, heat, or impact chemical disintegration.

2. A liberation of electrons from a substance into a vacuum.

Since all substances consist of atoms and since all atoms contain electrons, any substance may emit electrons; usually, however, the term refers to the emission of electrons from the surface of a solid.

3. The freeing of electrons into space from the surface of a body under the influence of heat, light, impact, chemical disintegration, or a potential difference.