What are coronal holes in the sun?

Coronal holes generally discharge solar wind at a speed about twice the average. The escaping solar wind is known to travel along open magnetic field lines that pass through the coronal hole area. Since coronal holes are regions in the Sun’s corona that have much lower densities and temperatures than most of the corona, these regions are very thin. This thinness contributes to the solar wind since particles within the chromosphere can more easily break through.