Sagging means when someone wears their trousers or jeans just below the waist.
Sagging is mainly a male fashion. Women and girls' wearing low-rise pants in a manner that shows the females' G-string underwear or panties is not usually described as sagging. People who wear sagging trousers or pants are sometimes called "saggers".
The origin
The style was made popular by skaters and hip-hop musicians in the 1990s, although sagging may have gotten started as early as the late 1980s. It was later declared a symbol of freedom and being aware of fashion culture with many teenagers and young adults. It was also the symbol for rejection of the values in the mainstream society.
It is often said the style got started with the United States' prison system. In that system, belts are sometimes not allowed. There may also be situations wherein there is not enough clothing of the appropriate size.