A brown dwarf is a type of celestial object that is larger than a planet but smaller than a star. It has a mass between about 13 and 80 times that of Jupiter, which is not enough to sustain hydrogen fusion in its core like true stars do. Instead, brown dwarfs generate energy through the fusion of deuterium and lithium, making them unique in the universe. These objects are often referred to as "failed stars" because they do not reach the necessary conditions to ignite and shine like stars such as our Sun. Brown dwarfs can be found in various regions of space, often in star-forming regions, and they emit very little light, making them difficult to detect.