Picture of an enclosed sunken courtyard

Quick answer：

A sunken courtyard, also known as a sunken garden, is a courtyard that is lower than the surrounding ground level. It is enclosed by walls or fences, creating a private and secluded space. The design often incorporates plants, trees, and water features, making it a serene and visually appealing area. Sunken courtyards are common in traditional Asian architecture, particularly in China and Japan.