It stands for "Wild Card Games Back." In Major League Baseball, each league has three divisions (East, Central and West). At the end of the season, the top team in each division receives an invitation to compete in the first round of the playoffs, but the Wild Card chooses the fourth team. The WCGB statistic is most important in August and September, for determining which team (not already in first place in its division) has a shot at getting the Wild Card spot. For example, if your favorite team is second in its division, the WCBG figure will show how many games it is behind the Wild Card leader (at that point in the season) competing to receive that fourth invitation to participate in the division playoffs.