What is the difference between a seed and a grain?
A grain is a seed. Strictly speaking, a vegetable is the plant or the root (e.g. celery stalk or carrot) of a plant. The word is commonly used to include non-sweet fruit such as tomatoes, however, so let's include those for the purpose of this answer. With a tomato, you have the fleshy, juicy part that you eat and it contains the seeds.