In cricket, a bowler's economy rate is the average number of runs they have conceded per over bowled.
[1] The economy rate is typically more important in limited-overs cricket than in the longer Test match format.
The shorter forms of the game demand that bowlers (and fielders) restrict the flow of runs from the opposition to limit the total accrued by the point at which the overs run out, giving their own team a better chance of making the winning score.
However, there is a balance to be struck - a bowler with a high economy rate in a Test match is generally still aiding the batting side's total, while taking a wicket in limited overs matches usually helps the bowling team by slowing the run rate.
[4] Although styles of play have evolved over the years, and bearing in mind that limited-overs cricket is a more modern phenomenon, it is evident that bowlers' economy rates tend to be higher for shorter formats of the game.