Cooper pairs are pairs of electrons that are bound together at low temperatures in a superconductor. These pairs form due to an attractive interaction mediated by lattice vibrations, known as phonons. Unlike typical electron behavior, which is repulsive due to their negative charge, the pairing allows them to move through the material without resistance. In a superconductor, Cooper pairs condense into a collective ground state, enabling the flow of electric current without energy loss. This phenomenon is a key aspect of BCS theory, named after John Bardeen, Leon Cooper, and Robert Schrieffer, who explained superconductivity in 1957.