Bulb

A short, enlarged shoot system that has as parts a short stem in which the shoot internodes do not elongate, and one or more buds enclosed by fleshy leaves or leaf bases. May serve as a storage and/or perennating organ. Usually underground.
For the electrical device that produces light, see Lightbulb.
Shallots--a type of bulb that people use for food.

A bulb is the part of some plants, mostly under the dirt, that stores food while the plant is resting from growing (a storage organ).

Some well-known bulbs people grow to use as food are onions and garlic. Some bulbs grown for the decorative flowers are the lily, tulip, and some irises.

Some plant storage organs that are similar to bulbs, but have different names are, tubers, corms (swollen stems), tuberous roots, and pseudobulbs.