UDN can stand for: National Democratic Union (Brazil) (União Democrática Nacional), a political party that existed in Brazil between 1945 and 1965 Univision Deportes Network, a Spanish-language sports channel in the United States Ulcerative dermal necrosis, a disease of salmon and trout United Daily News, a Taiwanese newspaper IATA airport code for Codroipo civil airport in Italy Unique Device Name of the UPnP Device Architecture Undiagnosed Diseases Network, an NIH-funded study of intractable medical conditions that have eluded diagnosis University of Da Nang, a public university system in Vietnam