Refers to a physical place open to the public, or the state of being in a public setting. Often used in contexts of behavior, manners, or rules.
See also: 公の場
公共の場では静かにしてください。
Please be quiet in public spaces.
公共の場で大声で話すのは避けましょう。
Let's avoid talking loudly in public.
Compound of 公共 (public) + の (possessive particle) + 場 (place). A straightforward modern term.