In Washington state, a public agency is defined as: "Washington State counties, cities, school districts, fire districts, water & sewer districts, health districts, parks & recreation districts, transit districts, irrigation districts, library districts, port districts, public facility districts, public utility districts, housing districts, and other authorized special districts who use MRSC Rosters as their small public works and consultant roster system."
In other words, it's basically public services and organizations that serve the community.