From AMS Glossary
Coronal Hole (Coronal Hole High-Speed Stream)
Abbreviated CH (CH HSS).
An extended region of the solar corona; exceptionally low in density and associated with unipolar photospheric regions having open magnetic field topology. Coronal holes can be found from the solar equator to the poles, but they are normally largest and the most stable at or near the solar poles. They appear as dark areas in the solar corona when observed in extreme ultraviolet and soft X-ray imagery. They are a source of high-speed solar wind—known as high-speed streams (HSS)—and are often the source of many recurrent geomagnetic disturbances and occasional geomagnetic storms. A coronal hole HSS lifetime can range from months to years.
Space Weather Prediction Center, 2018: Coronal holes. Accessed 13 August 2018. Available at https://www.swpc.noaa.gov/phenomena/coronal-holes.
Term edited 13 August 2018.