Pomegranate juice is the juice of the pomegranate (Punica granatum), a softball sized, reddish fruit native to Iran and the Caucasus, but cultivated around the world for both ornamental and fruit-bearing reasons. The pomegranate is an ancient fruit, mentioned in the Bible and the Qur'an. The pomegranate was also known to the ancient Greeks.
The only part of the pomegranate that is edible are the arils, a collection of around 600 small red fruits that look like popcorn kernels that are suspended in white, astringent pulp in the interior of the pomegranate. Pomegranates are generally cut in half and pressed to crush the arils and extract their juice.
Pomegranate juice is both tart and astringent, with a strong red berry flavor. Pomegranate juice can be cooked down to make grenadine (from the French word for pomegranate -- grenade), and cooked down further to make pomegranate molasses, which is a staple of Persian cooking. POM Wonderful is a common brand of pomegranate juice.