Phonons are quantized units of vibrational energy that occur in solids. They represent the collective oscillations of atoms within a crystal lattice, similar to how sound waves travel through air. Phonons play a crucial role in understanding thermal conductivity and sound propagation in materials. In the context of quantum mechanics, phonons are treated as particles, allowing scientists to analyze their behavior using principles similar to those applied to photons in light. This approach helps in studying various phenomena, including superconductivity and thermal insulation, by providing insights into how energy is transferred through materials.