Large loop-like structures on the edge of the solar disk sometimes stand out brightly against the dark background of space. These enormous structures are called solar prominences.
Although prominences appear to be very bright and hot, they are actually much cooler and denser than the surrounding plasma in the Sun's corona (outermost atmosphere). Prominences are shaped by the Sun's complex magnetic field, often forming loops with each end "anchored" to the Sun's surface (photosphere). Prominences are enormous, extending for many thousands of kilometers (miles).
Prominences can last for several days - or up to several months! Some prominences erupt and break apart, giving rise to coronal mass ejections (CME).
Sometimes we see prominences against the bright background of the Sun itself, instead of at the edge of the Sun's disk. These prominences appear dark compared to the bright background of the Sun, and are called solar filaments. Prominences and filaments are really the same type of phenomena; they just have different names due to how they look because of their positions and backgrounds.