OK I HAD TO LOOK IT UP ! HERES A WEB SITE THAT GETS ALL INTO IT ! I GOT BORED AFTER THE 1ST TWO LINES !! LOL
Instant Center
All vehicles have a specific point around which the entire car will balance called the center of gravity (CG). For most domestic front-engine, rear-drive cars, the CG is generally located forward of the mid-point of the car at around camshaft height off the ground. While all rear suspensions pivot around a given point, this is not necessarily the point at which the rear suspension applies power or lift. Suspension engineers call this lift point the instant center (IC). Different suspensions place this IC at different positions in the car. Because suspension components tend to shift as the body lifts or squats, this position is dynamic, meaning that it moves as the car pitches or rolls. One definition of IC is the unseen center of an arc created by the moving suspension links. The simplest instant center is a drag race ladder bar. The forward mounting point for the ladder bar where it hooks to the chassis also happens to be its instant center. With other rear-suspension designs, the instant center is an imaginary point in space
http://www.speed-wiz.com/calculations/suspension/index.htm