Cách sử dụng
The word 'underground' is often used to describe things that are hidden or secret, or things that are located below the surface of the ground. For example, a subway system is often referred to as the "underground" because the trains run on tracks that are located below the surface of the streets. The word can also be used to describe things or activities that are outside of the mainstream or not widely known, such as underground music scenes or underground parties. In general, the word 'underground' describes something that is not easily visible or accessible, or that is kept hidden from mainstream society.