Fielding percentage (aka Fielding average, FP, FA) is a common, though limited, measure of fielding effectiveness. Fielding percentage is calculated as chances accepted divided by total chances, and thus measures how effective a fielder is in avoiding errors.
For much of baseball history, fielding percentage was used as the primary measure of a fielder's ability. Despite its popularity, fielding percentage has long been criticized for counting only one class of fielding failure while ignoring others; it penalizes fielders for mishandling balls that they get to, but does not penalize them for failing to get to balls in the first place. It thus rates slow but sure handed fielders ahead of far ranging but less sure handed ones.