The MacPherson Nebula, a supernova remnant
A supernova remnant was a gaseous structure resulting from a star exploding in a supernova. Examples include the MacPherson Nebula and Arachna. (TNG: "Emergence"; TAS: "The Terratin Incident")
In July of 2151, Enterprise NX-01 detected a J'ral class supernova remnant approximately three light years off their course. However, they opted to study another nearby object instead. (ENT: "Civilization")
The Briar Patch was flooded with radiation from supernova remnants. (ENT: "The Augments")
In 2375, Captain Kathryn Janeway used studying a supernova remnant as an excuse for entering a restricted part of Devore space. (VOY: "Counterpoint")
The Crab Nebula is another supernova remnant. Supernova remnants are often denoted as SNR. As such, SNR 093120 might be another example of a supernova remnant.