I know what camber and toe are. But I don't know what caster is.

 

Caster is the degree (+/-) that the suspension fork/components faces front to rear. Think of it as: is your wheel closer or farther away from the firewall?

For other people who don't know:
Toe is the amount of degree (in a 360*) that the front of the wheels face away or towards each other from the center of the car. Simply, spread, spaced boobs, or tight, close boobs.

Camber is the degree the vertical position of the suspenion/wheels are. Simplicity purposes, how much the top of your wheel is closer to or farther away from the center of your car.

 

Ah, gotcha. I've got a clear picture now. Thanks.

 

A good introduction to the topic:

Link: Camber, Caster, Toe-in