What is the signifigance of the "black spot" ?

Pirates are presented with a "black spot" to officially pronounce a verdict of guilt or judgment. It consists of a circular piece of paper or card, with one side blackened while the other side bears a message and placed in the hand of the accused.[1] It was a source of much fear because it meant the pirate was to be deposed as leader, by force if necessary--or else killed outright.