Region of influence
From AMS Glossary
region of influence
The domain of air that is modified by an embedded object.
For example, consider a steady wind with straight streamlines well upstream of an isolated building. As the air nears the building it will diverge to flow around the building, eventually converging behind the building and becoming straight again. The domain where the streamlines are affected by the building is the region of influence. Similar regions can be found for flow around mountains, airplanes, and weather instruments.