Bitter orange, also known as Citrus aurantium, is a fruit that originates from Southeast Asia. It is characterized by its small size, bright orange color, and a distinctively tart flavor. The fruit is often used in cooking, particularly in marmalades and sauces, and its peel is used to make essential oils. The tree that produces bitter orange is also valued for its fragrant flowers, which are used to create neroli oil. Additionally, bitter orange is sometimes included in dietary supplements for weight loss, although its safety and effectiveness are still under research.