Before coffee beans are roasted, they are known as “green beans.” The green beans are actually green, but there is some variation in color, so the name comes both from the color and from the fact that they need to be roasted before being brewed to bring out their coffee flavor. Green coffee beans contain caffeine and there has been a interest recently in harvesting that caffeine without the coffee flavor associated with it. Green coffee extract is the result of this process.
The extract is extracted from the coffee beans using a variety of (probably proprietary) methods and what you’re left with is a highly caffeinated substance with very little flavor. It is added to energy drinks and used as a nutritional supplement, and some even promote it as helpful supplement to take when trying to lose weight.