Definition & Meaning of "one's jaw drop (open)"in English

What is the origin of the idiom "one's jaw drops" and when to use it?

The idiom "one's jaw drops" originates from the physical reaction of a person's jaw literally dropping when they are astonished or surprised. This expression is used to describe a state of shock, disbelief, or amazement. This expression is commonly used in everyday conversation to emphasize the magnitude of one's surprise.