[[File:Calcite and polarizing filter.gif|thumb|300px|Printed label seen through a double-refracting calcite crystal and a modern polarizing filter rotated to show the different polarizations of the two images.]]
The term ''polarization'' was coined by [[Étienne-Louis Malus]] (pronounced {{respell|ma|LOOSE|'}}) in 1811.{{r|buchwald-1989|p=54}} In 1808, in the midst of confirming Huygens' geometric description of double refraction (while disputing his physical explanation), Malus had discovered that when a ray of light is reflected off a non-metallic surface at the appropriate angle, it behaves like ''one'' of the two rays emerging from a calcite crystal.{{r|buchwald-1989|p=31–43}} As this behavior had previously been known exclusively in connection with double refraction, Malus described it in that context. In particular, he defined the ''plane of polarization'' of a polarized ray as the plane, containing the ray, in which a principal section of a calcite crystal must lie in order to cause only ''ordinary'' refraction.{{r|buchwald-1989|p=45}} His definition was all the more reasonable because it meant that when a ray was polarized by reflection (off an isotopic medium), the plane of polarization was the plane of incidence and reflection — that is, the plane containing the incident ray, the normal to the reflective surface, and the polarized reflected ray. But, as we now know, this plane happens to contain the ''magnetic'' vectors of the polarized ray, not the electric vectors; the component of the electric vector normal to that plane (i.e., parallel to the surface) is reflected to some extent for ''any'' angle of incidence, due to the change in [[permittivity]] at the surface.
The modern implication of Malus's definition — that the plane of polarization contains the ''magnetic'' vectors — survives in the online Merriam-Webster dictionary.{{r|merriamW}}
