earned' run' av"erage
a measure of the effectiveness of a pitcher, obtained by dividing the number of earned runs scored against the pitcher by the number of innings pitched and multiplying the result by nine. A pitcher yielding three earned runs in nine innings has an earned run average of 3.00. Abbr.: ERA, era
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.