Meaning of fine structure

fine' struc'ture

Pronunciation: (fīn), [key]
— Physics. Physics.
  1. a group of lines that are observed in the spectra of certain elements, as hydrogen, and that are caused by various couplings of the azimuthal quantum number and the angular momentum quantum number. Cf. hyperfine structure.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.