An open golf tournament usually refers to a golf tournament in which all golfers are eligible to play regardless of their professional or amateur status.
Some amateur-only tournaments are also described as open, although by definition professional golfers are excluded.
Any golfer can, in theory, play in The Open either by invitation or by various forms of qualification.
In practice, the event is a professional tournament in which a small number of the world’s leading amateurs also play, by invitation or qualification.
[2] This is a list of the national Opens that have featured on the principal tours.