PAO was a department, division, or position within Starfleet's Fleet Operations Center on Earth. (ENT: "Demons" set artwork)
In January of 2155, Starfleet officers J. Van Over and D. Sperber worked in (or as) PAO.
PAO was seen on directory listings seen on the set of "Demons".
, like many of the other divisions, departments, or positions on the listing, is a reference to NASA
terminology, in this case, the "Public Affairs Officer".