What’s the difference between a grain and vegetable?

I should have seen that one coming! Thanks, reader Clare. Grains are the seeds of grasses. Vegetables are…well, there isn’t a strict definition of what vegetables are. A vegetable can be any edible part of a plant that’s not a) the seed or b) the ripened ovary. The ripened ovaries of seed-bearing plants are what are known in scientific terms as “fruits”, if you follow me. Thus you can see why tomatoes and squash are classified as fruits and not a vegetables: they have seeds.