Cal. Gov. Code § 56075

“Special assessment district” or “assessment district” means an area fixed, established, and formed by a city, county, district, or the state, pursuant to general law, special act, or charter, that is specially benefited by, and assessed, or to be assessed, to pay the costs and expenses of, acquiring any lands or rights-of-way, acquiring or constructing any public improvements, maintaining or operating any public improvement, or lighting any public street, highway, or place.