Orange juice is, at its most fundamental, the juice squeezed from fresh oranges. It has developed into a commercial product, and a variety of types are available.
Fresh orange juice is simply made by squeezing or reaming a fresh, cut orange to extract the juice. It is not very stable and must be chilled and consumed within a few days.
Concentrated orange juice is strained, pasteurized, concentrated, and frozen. This process extends its shelf life, and it can be re-diluted with water before using.
Pasteurized "not from concentrate"Edit
This variety of orange juice is commonly available in the refrigerated section of grocery stores. It is pasteurized and stored aseptically, and it is sold ready-to-use.
Canned orange juice is heated before storage in metal cans. It is shelf-stable for a long period of time, although it loses flavor with age.