Never heard the term before so with your guidance: "In wheel alignment Steering axis inclination (SAI) is the angle from the vertical defined by the center line passing through the upper and lower ball joints. Usually ..."
I'm a few steps away from working with that myself.
Lee
And yes, what I said about dirty words using abbreviations like that has created big problems before. The company I worked for uses coding for certain things and one (that I know of) the coding turned out to be a very dirty word in one language and almost caused a big problem. The probable solution was not to include vowels (including "X" and "Y") in the coding.