I wondered about that too. But I used the internet to find the answer just now.
It turns out the harmonic series is very closely related to music (harmonics) even more so than a redneck and his wife. Here.Originally Posted by Wikipedia
On the same note (get the pun ), why are "harmonic functions" called "harmonic".
Somebody asked me this a long time ago. I made a guess that the Laplacian equation describes the motion of a wave, hence the name harmonic. But now I know that I was wrong. Because the Laplacaian equation appears everywhere in mathematical physics. Both the heat and wave equations have contain this del-squared operator in the PDE along with over equations, so my initial explanation is totally wrong.