Phonon dispersion refers to the relationship between the frequency of phonons and their wavevector in a material. Phonons are quantized modes of vibrations in a solid, and their dispersion can provide insights into the material's elastic properties and thermal conductivity. The dispersion curve illustrates how the energy of these vibrational modes changes with different wavelengths. In a phonon dispersion diagram, the x-axis typically represents the wavevector, while the y-axis shows the frequency. Different materials exhibit unique dispersion relations, influenced by factors such as atomic mass and bonding strength. Understanding phonon dispersion is crucial for applications in solid-state physics and materials science.