You can eat what is above ground if you have a garden. If you get your cauliflower at the store - I usually peel off some of the pieces that look like leaves real tight against the stem, and eat the rest ~ raw or cooked.
ANS 2 - Excellent answer above, just to add to that, the stalk is a very good starter for veg soup if chopped finely. - I often make 'Groontiesoop', a Boer variety of vegetable soup, using cauli and broccoli stalks. Everyone loves it.
All of it can be eaten. Florets as a veg or in salad and the stem and leaves in a soup.
A cauliflower is a flower.
It is the head.
Flower
Cauliflower is the flowering part of the plant.
It is part of 'brassica'.
Cauliflower Root, leaf or flower The name 'Cauliflower' means Cabbage Flower.
There is a top plant and then the cauliflower among the leaves, so it doesn't grow underground but on top. Cauliflower plants do send roots underground, but the flowers, the parts that are eaten, grow above ground.
Flower Condensed inflorescence
The florets, - the bits of the head.
It is a plant in it's own right, not part of anything else.
No, I believe it's the stalk and leafy part of the plant.