Summary: Defensive Ratings - what makes up the defensive player
Range measures how much ground a player can cover on the field. If you've got great range, you get to more batted balls than other players do. Translation: more potential outs. Consider a centerfielder with great range - he'll catch more fly balls than a lesser centerfielder. Range up the middle (SS, 2B, CF) is typically the most valuable.
''Famous players with high Range: Willie Mays, Ozzie Smith ''
"Soft hands" - can you catch the ball or not? A player with a good glove makes less errors. One funny consideration is high Range and low Glove - you get to more balls in play, but fumble more of them. An interesting tradeoff. Glove is a factor of fielding the ball (once you get to it) and transfering it to your throwing hand cleanly.
''Famous players with high Glove: Brooks Robinson, Ryne Sandberg ''
A combination of how hard, far, and accurate a player can throw. For outfielders, this has a significant impact on the frequency and success rate of runners trying to tag up and take extra bases. For infielders, this can impact the success rate of double plays. Catchers, of course, need a good arm to throw up baserunners trying to steal. In all cases, Arm can also contribute to errors, though the majority of errors are caused by the Glove rating. Note that Arm is not a factor of pitch speed!
''Famous players with high Arm: Dave Winfield, Ivan Rodriguez ''