Bracket racing is a competition between two cars, where the slower car leaves first, and the faster car leaves later by the difference in the declared times of the cars. This would theoretically have both cars cross the line at the same time. The purpose being to have a fair competition between two cars having one faster than the other. In a perfect world, there would be enough cars that were close equals competing against each other, but at amateur races it isn't the case.
This differs with match racing, where both competitors would leave at the same time in a "heads Up" race.