Ultracool dwarfs are a subclass of low-mass stars known for their extremely low temperatures and faint luminosities. These stars have effective temperatures below 2,700 K and are commonly observed in spectral classes M, L, T, and Y. Ultracool dwarfs are of particular interest in the field of astronomy because they represent a transition between stars and brown dwarfs, which are substellar objects that do not undergo nuclear fusion. Research on ultracool dwarfs focuses on understanding their atmospheres, evolution, magnetic activity, and formation mechanisms. Their study also provides valuable insights into the properties of planetary atmospheres and the potential for habitability in exoplanetary systems.