It's named after Mir Osman Ali Khan, the last Nizam of Hyderabad; a popular story says his kitchens created it for him, though the exact origin is unrecorded.
A dough of flour, milk, ghee, cardamom, sugar, and a pinch of salt is baked into a soft, crumbly biscuit that dissolves almost the moment it's dunked. Hyderabad's Irani cafés sell it by the piece as the standard accompaniment to a glass of Irani chai.