Agility is basically how fast and accurate you are in your movements. A character with high agility attacks faster and more accurately, and Agility helps defend against physical attacks. Low agility, of course, makes you slower and less accurate. An Elf will hit far more often than a Half-Ogre, though a Half-Ogre's incredible crushing blows may compensate. Agility is a component of most skills, and is extremely useful for a thief. A thief with high agility will have very good skills! Again, Agility is a necessary stat for any fighting class, and is useful for magic-users to direct offensive spells.