Ultra-diffuse galaxies (UDGs) are a class of galaxies that are characterized by their low surface brightness and large physical size. They were first identified in the 1980s, but it wasn't until the last decade that they became the focus of significant research attention. UDGs are typically as large as spiral galaxies, but with much lower luminosities, making them difficult to detect and study. They are found in a variety of environments, from galaxy clusters to isolated systems, and their origins and properties are still not well understood. Research on UDGs is aimed at understanding their formation and evolution, as well as their role in the broader context of galaxy evolution. Some theories suggest that UDGs may be the remnants of more massive galaxies that have been stripped of their outer layers through interactions with other galaxies or the surrounding environment. Studying UDGs is challenging due to their faintness and diffuse nature, but advances in observational techniques and theoretical models are helping to shed light on these enigmatic objects.