What is the difference between Marijuana and Hemp?

Marijuana and Hemp are commonly known names of the plant species Cannabis Sativa. So, a simple scientific answer would be there is no difference in plant species as it is the same plant.

Now, when speaking of the law there is a difference between marijuana and hemp.

The legal definition of marijuana according to United States law is all parts of the plant Cannabis sativa L., whether growing or not; the seeds thereof; the resin extracted from any part of such plant; and every compound, manufacture, salt, derivative, mixture, or preparation of such plant, its seeds or resin.

Such term does not include Hemp which is the mature stalks of such plant, fiber produced from such stalks, oil or cake made from the seeds of such plant, any other compound, manufacture, salt, derivative, mixture, or preparation of such mature stalks (except the resin extracted therefrom), fiber, oil, or cake, or…