Coronal Hole

An extended region of the corona , exceptionally low in density (large open "gaps"), and associated with photospheric regions. Coronal holes are closely associated with those regions on the Sun that have an "open" magnetic geometry, that is, the magnetic field lines associated with them extend far outward into interplanetary space, rather than looping back to the photosphere . Ionized material can flow easily along such a path, and this in turn aids the mechanism that causes high speed solar wind streams  to develop.