The rotating table tray many dim sum restaurants use is called a Lazy Susan.
Placed in the center of a communal table, the turntable lets diners bring shared dishes and tea within reach without leaning across one another. This is particularly useful at dim sum, where several small plates and bamboo steamers arrive for the whole group rather than for one individual.
Lazy Susans are commonly made from glass, wood, or plastic and can rotate on a central bearing. They are not a serving trolley: a trolley is pushed around the dining room by staff, while a Lazy Susan stays on the table and is turned by diners.
The device is also used in other Chinese restaurant settings, though it is not uniquely Chinese and its exact origin is debated. At a dim sum meal, etiquette often favors rotating it carefully, especially when someone is taking food, and showing consideration for older diners or guests who have not yet been served.