Error
An fielder records an error when they fail to make a play that they should have made with common effort, and then the opposing offense benefits as a result of such a mis-play.
The error is the most simple defensive statistic, and of course, the most widely used. Like many other such stats, it lacks the independence from other teammates' performances. Many errors are given to players that did not correctly catch the ball, yet the ball was not thrown to them in the right manner in the first place.
Errors are the lone statistic used in determining fielding percentage which is the major factor in determining the Gold Glove awards.