The chemical shift (symbol: δ; units: ppm) of a nucleus (eg: 1H, 13C) in a molecule is a measure of how shielded (see shielded nucleus) or how deshielded (see deshielded nucleus) the nucleus is when the molecule is in an external magnetic field. The higher the chemical shift of a shielded nucleus, the less shielded the nucleus. The higher the chemical shift of a deshielded nucleus, the more deshielded the nucleus. Or, if two nuclei in the same molecule have different chemical shifts, the nucleus with the higher chemical shift is deshielded; the one with the lower chemical shift is shielded.
eg: methyl acetate (1)
The shift of Hb is higher than that of Ha, meaning Hb is less shielded than Ha, or Hb is deshielded and Ha shielded.
see also upfield, downfield