An Etymological Dictionary of Astronomy and Astrophysics

A bright cloud-like feature that appears in the vicinity of a sunspot. Plages represent regions of higher temperature and density within the chromosphere. They are particularly visible when photographed through filters passing the spectral light of hydrogen or calcium.

Etymology (EN): From Fr., from It. piaggia, from L.L. plagia “shore;”
noun use of the feminine of plagius “horizontal;” frpm Gk. plagios “slanting, sideways” from plag(os) “side” + -ios adj. suffix.

Etymology (PE): Plâž, loan from Fr., as above.