[Black Gram, Black Lentils, White Lentils (India); Vigna mungo]
These small black beans native to India are the same size and shape as the familiar Mung Bean, and are one of the more important beans/dals in India.
Urad beans are sold in several forms, whole (Urad, Black Gram), Split, split and peeled (Urad Dal, White Lentils) and also whole peeled (less common).
Crushed urad beans are also used as an ingredient in spice mixes, generally fried or roasted with other spices before being added to the main recipe, either as an ingredient or as a garnish (tempering, tadka).
More on Varieties of Bean.
Buying: Whole urad beans, split urad beans and dal (split and peeled) are easily available in markets serving Indian communities.
Storing: Keep beans or dal cool and dry in a sealed container and mark the container by date purchased. Technically they'll last for years without spoiling - BUT in practice a year is maximum. With age they cook less and less well until they simply will not soften, no matter how long you soak them and how long you cook them.
Soaking: Whole urad beans need to be soaked in lightly salted water at least 4 hours and preferably 5. You'll need 2-1/4 cups of soaking water for every cup of beans. The dal should be soaked for at least a half hour, but if it's old even a couple hours won't help much.
Cooking: Whole soaked beans will cook in about 45 minutes. Unsoaked they'll need at least an hour, proably more, and they tend to fall apart a lot more than soaked beans. Soaked dal should be cooked for around 1/2 hour depending on how soft you want it. In India it's normally cooked until like a thick soup, but if the dal is old it will never soften.