Definition: "1-2-3 Best Ball" is a competition format for 4-person teams. Each player on the team plays his own ball throughout the round. On each hole, a predetermined number of the lower scores is used.
One the first hole, the lowest score among the four players counts as the team score. On the second hole, the two lowest scores become the team score. On the third hole, the three lowest scores become the team score. On the fourth hole, it's back to the one lowest score, and so on throughout the round.
1-2-3 Best Ball is a good way to keep all the players involved in the fate of their team.