Bitter orange, Seville orange, sour orange, bigarade orange, or marmalade orange refers to a citrus tree (Citrus × aurantium) and its fruit. It is a hybrid between Citrus maxima (pomelo) and Citrus reticulata (mandarin). Many varieties of bitter orange are used for their essential oil, and are found in perfume, used as a flavoring or as a solvent. The Seville orange variety is used in the production of marmalade.