In
mathematics, a number of concepts employ the word
harmonic. The similarity of this terminology to that of
music is not accidental: the
equations of motion of vibrating strings, drums and columns of air are given by formulas involving
Laplacians; the solutions to which are given by
eigenvalues corresponding to their modes of vibration. Thus, the term "harmonic" is applied when one is considering
functions with
sinusoidal variations, or solutions of
Laplace's equation and related concepts.