It probably encompasses much more than what I am doing, but I still use the term to describe it.
Basically, if I know that I want the foot of one leg to be in a certain position, I can use algebra and trigonometric functions to calculate the angles of each joint that will put the foot in that position.
If I get a chance, I will write up a description of the formulas I am using.
It was a lot of fun using my dormant math skillz ;D