ERA. A baseball statistic. The average number of earned runs allowed (by a pitcher) per nine innings pitched. A semi-meaningful statistic, since the actual pitching conditions encountered by two different pitchers may be an apples and oranges situation. If you pitch for the Colorado Rockies, your stats are bound to look bad, since you pitch half your games at Coors Field, at mile-high altitude. It's a liability if you're about to negotiate your next long-term contract.