white spot
/ˈwʌɪtspɒt/noun
1Any of several Eurasian moths having a prominent white marking on the forewing; (in later use) specifically the European noctuid Hadena albimacula.
2 Astronomy. A distinct white area observed by telescope on the surface of a planet; (in later use) specifically such an area occurring periodically on Saturn or Jupiter, now attributed to violent atmospheric disturbances.
3More fully white spot disease. A disease affecting fish in aquariums, hatcheries, and fish farms, characterized by the development of small white spots on the skin and gills, and caused by the ciliate protozoan parasites Ichthyophthirius multifiliis (in fresh water) and Cryptocaryon irritans (in salt water).
4In South Africa under apartheid: an area occupied by white people and surrounded by areas officially designated for black occupation; especially a white-occupied area within one of the black ‘homelands’. Compare black spot. Now historical.
Origin
Mid 18th century; earliest use found in Moses Harris (1730–c1788), entomologist and artist. From white + spot.