An ugli fruit is a citrus fruit created by hybridizing a grapefruit (or pomelo according to some sources) and a tangerine. Its species is Citrus reticulata x Citrus paradisi.While googling, I also stumbled on this.
Native to Jamaica, the fruit was first bred in Brown's Town in 1914. It got its name from the unsightly appearance of its rough, wrinkled, greenish-yellow skin, wrapped loosely around the orange pulpy citrus inside. An ugli fruit is slightly smaller than a grapefruit and has fewer seeds. It tends towards the sweet side of the tangerine rather than the bitter side of its grapefruit lineage, with a fragrant skin. The fruit is seasonal from December to April. It is distributed in the USA, UK and Europe between November and April, and is on occasion available from July to September.
Americans pronounce the name "ugly," but in Jamaica, where it is grown, its name is pronounced /ˈhu.ɡli/.