"bumpsteer : toe change during the supsension cycle which can cause the vehicle to dart side to side. This is caused by the steering linkage moving in a different arc than the suspension."
See other definitions here:
http://www.desertrides.com/reference/terms.php
The shims angle the axle (well, actually the kingpin) rearward meaning it results in more negative caster. This causes the wheels to want to return to center more easily or quickly after steering left or right. It changes how the wheels "track".
I was taught in high school MANY moons ago to remember "caster" by thinking of your arm motion when you cast a fishing pole. Forward and back, get it?
Camber is the top of the tire tilting in or out, toward or away from the vehicle.
Toe - is how the front of the tires point. Totally straight ahead (neutral), slightly toward each other (toe-in) or away from each other (toe-out)
Hope this helped.