From BR Bullpen
The shape and size of the outfield varies from ballpark to ballpark, contrary to the infield whose size and shape are set in the official rules. The rules only specify a minimum distance for the placement of the outfield fence. At the furthest edge of the outfield, at the base of the fence, is the warning track.
There are normally three players charged with fielding duties in the outfield: the left fielder, the center fielder and the right fielder. They are known as the outfielders. Normally, the center fielder needs to be the speediest and rangiest of the three, as in most ballparks, the center field area is the largest; the right fielder needs to have a strong throwing arm, in order to prevent baserunners from going from first base to third base on a single.
The term outfield is also used to refer collectively to the three outfielders, e.g.: team x has a very fast outfield.