As a verb, to bean is to hit someone on the head with an object.
As a noun, a bean is a food source. Beans are the seeds of legumes of the family Leguminosae, also known as pulses; peas are also members of this family, and I confess I have been unable to determine the difference between beans and peas. (Peas have round seeds? Though this seems very trivial, and it's just a wild guess.) In any case, beans have edible seeds and seed pods and are a very ancient food source which has been consumed by humans for thousands of years.
Before the "discovery" of America, Europeans didn't have many types of beans except for broad beans; they learned about soybeans from Asians, and most of the rest they got from First Nations people, who had already developed most of them on their own. (Compare corn and squash, also developed by indigenous North Americans, and making up their important culinary trinity, fondly known as Three Sisters.) Most beans grown today are annuals (though some Asian varieties are perennials) and grow erect (bush types) or as vines (running or pole types).
In relation to the culinary arts, the life of the green bean (I'm talking here of that pod and its seeds, not the whole plant) passes through several stages.
In the early days of the bean's life, up until about a week, the pod of the bean is tender enough to be eaten, and the seeds in the pod are so small that they are easily overlooked. Young bean pods generally snap when folded, and so at this stage beans may be called snap beans or just edible pod beans. Varieties include the rounded, skinny French bean or haricot vert; the rounded, thicker string bean, named for the tough string that used to run along its length but which has now been mostly bred out; the broad, flat runner bean; the long, thin Asian yard long green bean; and the wild and wonderful wing bean. On the pea side of the divide (if divide it so is) lie snow peas and sugar snap peas. Though most edible pod beans are green beans, there are also yellow and purple varieties; wax beans, for example, may be green or yellow. Beans grow easily and produce lots, or you can buy them all through the summer; choose crisp, bright-coloured, blemish-free beans and store them in a plastic bag in the fridge. Ideally, edible pod beans should be used within a few days. They're great steamed, blanched, or stir fried.
As the bean matures, the seeds inside swell and become visible through the skin; at this stage the pod is tough and leathery but the beans themselves are delicious morsels. These babies are often called shell beans or just shellies. Shell beans include lima beans, butter beans, fava beans, and cannellini and flageolet beans (varieties of kidney beans); on the pea side, it's your basic green peas. Soybeans have become a popular item too as a shellie, steamed in their shells and then shelled and eaten; you'll see them in Japanese restaurants as an appetizer called edamame. Store shellies as for edible pod beans, and note that they'll taste better if you buy them in their shells and extract them yourself. If you buy them shelled, cook them as soon as possible. Shellies are very good braised in broth, butter, or chopped tomatoes and herbs. They are also very nice steamed or blanched; if prepared in this way, you can substitute them for cooked dried beans with delicious results. Shellies have the advantage of freezing well.
As the bean matures nearly all its moisture evaporates; the pod becomes dry and brittle and eventually, left to its own devices, bursts open, scattering the seeds which will become future bean plants. At this stage our friends are known as dried beans. There are many kinds of dried beans available, which isn't surprising considering that they store so well. Don't be fooled, though; they don't keep indefinitely: more than a year and they're stale - throw 'em out and buy fresh. Azuki, adzuki or adsuki beans are small mild beans used to make red bean paste, so popular in Asian desserts; they and black-eyed peas are members of the mung bean family, a group of dried beans that are popular as sprouts. (Dried beans of most varieties make great sprouts, smaller ones working best; ideally the beans should be relatively fresh and, in a perfect world, organic.) Black beans are tasty babies, as are the various kidney bean types: red, cannellini, and flageolet. Chick peas or garbanzo beans, lentils, fava beans, Great Northern beans, pinto beans...well, you get the picture: there's lots of types of dried beans, and the peas are not to be forgotten, with split peas weighing in on their side. Cooking times vary depending on whether or not you soak them first (if you do, they'll cook faster), the size of the bean, the thickness of the skin, and whether or not they're split. Once cooked, they can be braised, baked, stewed, sauteed, or fried (or refried); they're great in soup and can be cooled and served in salads; and they get along well with rice and other grains as well as all types of meat and many vegetables. In a word, and like their fresh predecessors, dried beans are a versatile lot.
I have been asked, but I don't know, how many bean varieties are enjoyed in all three forms. I notice substantial cross-over between shellies and dried beans, though.
Beans are very nutritious. Dried beans are popular with vegetarians because they contain a lot of protein; this makes them good meat substitutes, if you want to look at them that way. Beans are high in fiber, rich in nutrients, and relatively low in calories. Because they are digested slowly, they raise the blood sugar slowly, making them suitable for diabetics. And there's one other thing beans are famous for: flatulence. It's caused by complex sugars that are only present in dried beans; edible pod beans and shellies will not cause this particular problem. (Discarding the soaking water from dried beans, or soaking canned beans for an hour and then discarding the soaking water, will help reduce the flatulence factor.) Still, you gotta love beans, farts or no.