'Shield tunneling' is a modern underground construction method used to dig tunnels safely through soft, unstable, or water-bearing soil. The term combines two characters: 盾 (dùn), meaning 'shield', refers to the large, cylindrical, movable steel shield that protects workers and supports the tunnel face; and 构 (gòu), meaning 'to construct' or 'to build', indicating the engineering process itself. Together, 盾构 describes both the machine (the shield tunnel boring machine) and the method it enables.

This technique is widely used in China’s rapid urban metro expansion, especially in cities with complex geology like Shanghai and Guangzhou. It minimizes surface disruption, reduces risk of collapse, and allows precise alignment and lining installation in one continuous operation. While the word sounds technical, it appears frequently in infrastructure news, engineering reports, and public announcements about subway projects.