Photoemission is a process in which electrons are emitted from a material when it absorbs light or electromagnetic radiation. This phenomenon occurs when photons, the particles of light, strike the surface of a material, providing enough energy to overcome the binding forces holding the electrons in place. This effect is commonly observed in metals and semiconductors, where the emitted electrons can be measured to study the material's electronic properties. Techniques like photoelectron spectroscopy utilize photoemission to analyze the energy levels of electrons, helping researchers understand the behavior of materials at the atomic level.