The term 'Pit of a Plum' refers to the hard, seed-like structure found in the center of a plum. This structure is also known as a nutlet and is composed of two parts: the endocarp and the seed. The endocarp is the outer layer of the nutlet and is made up of a hard, fibrous material. The seed is the inner layer and contains the embryo of the plant. The nutlet is edible and can be eaten raw or cooked.