Some basic terms you should know about war.
“Area of Operations (AO), is a geographic command subdivision of an overall conflict or theater; each AO generally has its own subordinate commander, its own supply lines (see Communications, Lines Of), its own forces and its own operational objectives (see Operations, below).”
https://acoup.blog/2022/03/25/miscellanea-a-very-short-glossary-of-military-terminology/