Information that is widely known, but not acknowledged openly. / (dated) Information that is not widely known, despite being freely available.

plural of open letter

(intransitive, transitive) To open. / (intransitive) To reveal oneself; to share personal information about oneself; to become communicative. / (intransitive) To commence firing weapons.

plural of open mind

present participle of lay open

(patent law, Japan and South Korea) To publish a patent for initial public review, prior to the formal application for registration. / (transitive) To expose or reveal (something).

(sports) An undefended goal. / An opportunity that is readily available.

(idiomatic) With enthusiasm, as if embracing

plural of can-opener

A bar at which drinks are served without charge, usually at a social event.