In solid-state physics, a quantum of lattice vibrational energy. In analogy to a photon (a quantum of light), a phonon is viewed as a wave packet with particlelike properties (seewave-particle duality). The way phonons behave determines or affects various properties of solids. Thermal conductivity, for instance, is explained by phonon interactions. Phonons also provide the basis for understanding superconductivity in certain metals.