coronal hole

This term is a specialized astronomical designation used primarily in solar physics. It describes a specific structural feature of the solar atmosphere where the magnetic field lines are open, allowing solar wind to escape more easily into space. Because of the lower density of plasma in these regions, they appear as dark patches when viewed through X-ray or extreme ultraviolet filters.

In a technical context, the term is used to explain the origin of high-speed solar wind streams. It is a descriptive compound noun; while "coronal" refers to the corona of the sun, the "hole" does not imply a physical void or a puncture in a solid surface, but rather a region of relative depletion and different magnetic topology.