A dumbwaiter is a small lift intended to carry objects rather than people. Dumbwaiters found within modern structures, including both commercial, public and private buildings, are often connected between multiple floors. When installed in restaurants, schools, kindergartens, hospitals, retirement homes or in private homes, the lifts generally terminate in a kitchen.
The term seems to have been popularized in the United States in the 1840s, after the model of earlier "dumbwaiters" now known as serving trays and lazy Susans.
It is the title of a play by Harold Pinter. The great thing about a dumb waiter is that he cannot answer back.