noun
drop-lid; lid placed directly on food
A wooden or metal lid that sits directly on simmering food, used in Japanese cooking to ensure even heat distribution and prevent ingredients from moving.
煮物を作るときは落とし蓋をすると味がよくしみます。
When making simmered dishes, using a drop-lid helps the flavors soak in well.
落とし蓋がないときは、アルミホイルで代用できます。
If you don't have a drop-lid, you can substitute aluminum foil.
蓋 is a general lid that covers a pot, while 落とし蓋 is a smaller lid placed directly on the food inside the pot.
Compound of 落とし (otoshi, 'dropping', from 落とす) + 蓋 (futa, 'lid'). The term describes a lid that is 'dropped' onto the food rather than placed on top of the pot.