Shimano offers their reels in different gear ratios. Different gear ratios perform better for different sitations. (PG) means "Power Gear" or "Low Gear" and offeres the least line retrieve per crank, but the most torque. (HG) stands for "high gear" which is the most common gear ratio on spinning reels. This allows you to gain more line per crank without sacrificing too much cranking power. Then you have (XG) which is "Extra High Gear" for working lures fast and keeping up with speedy fish.