Definition of reef heron in US English:

reef heron

noun

  • Either of two herons of tropical and warm temperate coastal areas, Egretta sacra, of south-east Asia and Australasia, and E. gularis, found from West Africa to India, each occurring in slate-grey and white colour phases formerly mistaken for distinct species.

Origin

Mid 19th century; earliest use found in John Gould (1804–1881), ornithologist and publisher.