Urad dal a protein rich dal. In English it is called as black gram lentil.
Used in Indian food as a fermentation agent.
In idlis and dosas the sponginess is achieved by soaked urad dal.
In ancient India, it was also used in preparation of intoxicating drinks.
All over India paapads made out of urad Daal are very popular
The golgappas used in paani puri also have urad dal as their ingredient which renders the round well puffed pooris.