Definitions for "Open Tournament"
In the early days of tennis, clubs held two types of tournaments: Closed, to which only club members were admitted, and open, which non-members could also enter. With the advent of professionalism, "open" came to mean a tournament that could be entered by amateurs and professionals alike. Today, all major tournaments are opens.
A tournament in which any eligible competitor can play, if they qualify
A tournament which is open to any player.