Final answer:
Atmospheric pressure is the term used to describe the "piling up" of air above a region.
Step-by-step explanation:
The "piling up" of air above a region is called atmospheric pressure. Atmospheric pressure is the force per unit area exerted on a surface by the weight of the air above it. When air molecules accumulate in a particular area, they exert pressure on the surface below, causing the air to "pile up".