A solar prominence is a massive loop of the sun’s plasma that hangs attached to the visible surface of the sun, forming perhaps within a day but lasting as long as several months, according to NASA. They come in a couple of different varieties, most notably eruptive prominences, which are more dynamic structures, and quiescent ones, which can become eruptive when a new prominence forms below them.

Prominences often appear reddish because their plasma can originate deeper in the sun’s atmosphere, in a layer called the chromosphere, which is characterized by hydrogen at high temperatures that emits red light.

I wondered what the hell those were. Wish the article had more information than it does.