The rotating part on top of an electric stove or countertop, used to spread heat evenly across its surface, is commonly known as a "rotating or revolving heat diffuser" or a "rotating heat distributor."
It is designed to help distribute the heat from the stove's heating element more evenly, preventing hot spots and providing consistent cooking temperatures across the cooking surface. This can be especially useful when using cookware with uneven bottoms or when cooking delicate dishes that require gentle, even heat distribution. The rotating heat diffuser helps to improve the stove's overall performance and cooking results.