I dont have a exact definition but, I would call it the pitch (angle) the tire sits on a horizontal plane (the ground). too much one way and the inners wear prematurely, too much the other has the opposite effect.

Maybe someone can refine my statement

2000 SVT Contour #1077/2150 MSDS Headers/B&M Shifter/H&R's/

1995 Contour SE V6 #????/Tons KnuProject, awaiting mass mods