To make sense of these anomalies in a systematic way, Copi et al. introduced “a novel representation of cosmic microwave anisotropy maps, where each multipole order ℓ is represented by ℓ unit vectors pointing in directions on the sky and an overall magnitude” The beauty of this scheme is that the CMB alone determines the multipole vectors, without reference to the coordinate system. This contrasts sharply with the more common aℓm representation of spherical harmonics, which depends strongly on the coordinate system. The coordinate-free, geometrical nature of the multipole vectors makes it trivially easy to test for alignments between modes (for example the quadrupole and octopole align with each other) and with external reference points (the quadrupole and octopole align with the CMB dipole).
The true discover (sic) of multipole vectors was James Clerk Maxwell in his 1873 Treatise on Electricity and Magnetism