A magnon is a quantized spin wave — a collective excitation of magnetic moments in a ferromagnet. Near k=0, the dispersion relation is quadratic: ℏω(k) = 2JS(1−cos ka) + 2DS ≈ JSa²k² + 2DS, where J is the exchange coupling, D is single-ion anisotropy, S is spin, and a is lattice spacing. This quadratic dispersion (unlike phonons' linear) means the low-T heat capacity from magnons goes as T^(3/2) — the Bloch T^(3/2) law. The gap at k=0 set by anisotropy D protects magnetic order. The Brillouin zone boundary at k=π/a shows the maximum frequency, and the group velocity v_g = dω/dk determines magnon transport.