The bitter orange tree gives us several different perfume materials. 

Petitgrain is made from its leaves (and often twigs, too). Its smell is leafy, woody, green, and bitter, with undertones of sweet orange and light florals.

The flowers can be made into neroli or orange blossom depending on how they are processed: neroli is made when the flowers are distilled as an essential oil, and orange blossom absolute is made when the flowers are solvent-extracted. Distillation also produces hydrosol, which is what’s left behind after the oil is skimmed off following steam distillation, and often that hydrosol is then processed into an absolute called orange flower water absolute. 

Neroli smells floral, but more green and woody than orange blossom, which has a higher indole content and a honeyed, heady floral character.

Orange essential oil is pressed from the peel of the fruit, and can come from the fruit of the bitter orange tree (Citrus aurantium) as well as other orange trees, usually Citrus sinensis.