If something sags, it hangs down lower than its regular position. Things that sag might feel a weight or some other force placed upon it.
The roof is sagging under the weight of a heavy snowfall.
The back end of the truck is sagging because it’s carrying a load of rocks.
The mattress that Todd sleeps on sags in the middle because its old and he’s kind of heavy.
Vanessa’s eyelids are sagging because she’s so tired.
The 90-year old woman who lives across the street has saggy arms. (The word "saggy" is an adjective.)
Retail sales at some brick-and-mortar stores are sagging because of competition from online retailers.
The word "sag" has recently taken on a slightly newer meaning in reference to fashion. Men who wear their pants very low below the waist are said to be "sagging."
Mario’s pants are sagging.
The teachers at his school have asked students not to come to school with sagging pants.
A man’s underwear is visible when his pants sag.
Sagging is popular among people who like to listen to hip hop.