A quadrupole or quadrapole is one of a sequence of configurations of — for example — electric charge or current, or gravitational mass that can exist in ideal form, but it's usually just part of a multipole expansion of a more complex structure reflecting various orders of complexity. Mathematical definition The traceless quadrupole moment tensor of a system of charges (or masses, for example) is defined as » Q_), where M is the mass of each hole, and x_i is the unit vector in the x… (More on Quadrupole)