The act or an instance of becoming open or being made to open. An open space serving as a passage or gap. A breach or aperture. A clearing in the woods. The first part or stage, as of a book. The first performance: the opening of a play. A formal commencement of operation: attended the opening of the new museum. Games A specific pattern or series of beginning moves in certain games, especially chess. An opportunity affording a chance of success. See Synonyms at opportunity. An unfilled job or position; a vacancy.