Buckwheat, or common buckwheat, is a plant cultivated for its grain-like seeds and as a cover crop. The name "buckwheat" is used for several other species, such as Fagopyrum tataricum, a domesticated food plant raised in Asia. Despite the name, buckwheat is not closely related to wheat, as it is not a grass.
Oatmeal is a product obtained by processing oats. It goes through the stages of steaming, peeling and grinding – that's why in the end the oatmeal has smooth, neat flakes. Such cereals are incredibly useful, they contain minerals and vitamins, without which the body cannot do.