A Cooper pair is a pair of electrons within a substance that are bound together by a particular force that can occur at low temperatures, the bound pair able to travel without resistance, the basis for superconductivity (electrical conductivity that lacks any electrical resistance, a phenomenon of some substances at very low temperatures). The paired electrons are within atoms (bound to nuclei), but easily shift to other atoms, the collective effect of many such shifts comprising electrical current. The physics of the net force creating the pairing is a quantum phenomenon. Among the factors producing it are the distortion of the atoms due to electric forces, allowed to become significant by the absence of the microscopic vibrations inherent in heat, and the fact that such a pairing of electrons produces a boson, less hindered by quantum mechanical limitations. The theory of Cooper pairs and their relationship to superconductivity is known as BCS theory for its developers, Bardeen, Cooper, and Schrieffer.
It is presumed that analogous Cooper pairs can form from protons or neutrons given the extreme conditions of high density, such as in compact objects and possibly within supernova. The formation and breaking of such Cooper pairs (PBF for pair breaking and formation) would produce neutrinos, presumed to be one cooling mechanism within neutron stars.