What is the black ball line?

The black ball line, also known as the "blackball line," is a historical maritime boundary that was used by British naval forces to signify the limit of their jurisdiction and control over the seas. It represented the point beyond which British ships could be stopped and searched for contraband or illegal activities, particularly during the 19th century. The term is also associated with the practice of "blackballing," where members of a club could vote against the admission of a candidate by casting a black ball, symbolizing exclusion.