Figure 1. The Humble Administrator's Garden in Suzhou. Source.
Figure 2. Round door at the Lingering Garden in Suzhou. Source.
Figure 1. Plum, orchid, bamboo, chrysanthemum Chinese painting by Zheng Xie. Source. This is an example of bird-and-flower painting, of which the Four Gentlemen are a common theme. TODO date.
The literal Chinese name says it all: "Fake Mountain". The stones evoke the feeling of the beautiful rock mountains of China.
The term "奇石假山" (qi2 shi2 jia3 shan1, lit. "weird shaped stone fake mountain") is also used, almost as a synonym by many people, since the stones are often chose in interesting shapes. Choosing the right stone is basically an art form in itself.
The stones used are generally limestone, which as a sedimentary rock is weaker, and more likely to be eroded into interesting shapes.