Definition of "quadrupole"

quadrupole

noun
plural quadrupoles
1. (physics) A distribution of either electric charge or magnetization equivalent to two dipoles that point in opposite directions.
  Quotations
  Consider a linear quadrupole consisting of a point charge of strength 2q at the origin and point charges of strength —q at (0, 0, a) and (0, 0, —a).
  1975, David M. Cook, The Theory of the Electromagnetic Field, page 123
2. (physics) A magnet with two north poles and two south poles, used to focus a beam of particles.