In a metal lattice, the outermost shell electrons (often referred to as valence electrons) are not tightly bound to their parent atoms. These valence electrons are free to move throughout the metal lattice, creating a "sea" of delocalized electrons. These delocalized electrons are what give metals their characteristic properties, such as high electrical and thermal conductivity, as well as their shiny appearance.

In contrast to localized electrons, which are tightly bound to specific atoms, delocalized electrons can move freely within a material, contributing to electrical conductivity. The delocalized electrons in metals form what is known as a "Fermi gas" or a "sea of electrons," which is characterized by its continuous energy distribution and quantum mechanical behavior.