Flakiness is the quality of breaking into thin pieces or layers easily — the texture prized in pastry and in fish. In flaky pastry, flakiness comes from structure: thin sheets of dough separated by fat, which steam apart in the oven’s heat into distinct, shattering layers. In fish, it comes from anatomy: the muscle flakes — myotomes — separate along their natural divisions when the fish is perfectly cooked, the sign of a fillet done just right. Food scientists measure the force of fracture; cooks judge it by eye and mouth. The shared principle is weakness in the right places — layers or segments joined lightly enough to part cleanly. Whether in a croissant or a cod fillet, flakiness is structure designed to come apart beautifully.