Pappadom is a thin, crisp, disc-shaped food from the Indian subcontinent; typically based on a seasoned dough usually made from peeled black gram flour (urad flour), fried or cooked with dry heat. Flours made from other sources such as lentils, chickpeas, rice, tapioca, or potato can be used.
Papadums are typically served as an accompaniment to a meal in India, Pakistan, Bangladesh, Nepal, and Sri Lanka or as an appetizer or snack, sometimes with toppings such as chopped onions, chopped carrots, chutneys or other dips, and condiments. In certain parts of India, papadums which have been dried but not cooked are used in curries and vegetable dishes.
Pappad is called as Appalam in Tamil Nadu, pappadum in Kerala and pappad in most of the country.
Pappad is mainly manufactured in Rajasthan, Maharastra in the north and in the south, Kerala and TamilNadu in Madurai district and Kanchipuram and Chennai are major pappad or appalam manufacturers. It is called as ‘happala’ in Karnataka.
Papadum recipes vary from region to region and from family to family. They are typically made from flour or paste derived from either lentils, chickpeas, black gram (urad flour), rice, or potato.
Salt and peanut oil are added to make a dough, which can be flavored with seasonings such as chili, cumin, garlic, or black pepper. Sometimes, baking soda or slaked lime is also added. The dough is shaped into a thin, round flatbread and then dried (traditionally in the sun), and can be cooked by deep frying, roasting over an open flame, toasting, or microwaving, depending on the desired texture.
There are different varieties of papad like Chana, Moong, Urad, Potato, Rice, etc. Bikaner is the hub of Moong and Urad papad manufacturing. Potato Papad are made in Varanasi. Most sweets and snacks selling national companies are also involved into this business like Haldiram, Bikanerwala, Mishrambu, Lijjat, Shri Shyam Papad, etc.
In most curry houses in the United Kingdom and Australia, they are served as an appetiser with dips which often include mango chutney and lime pickle.
(Copied from https://en.wikipedia.org/wiki/Papadum)