Definitions for "Roll center"
the center about which body roll takes place during cornering. The position of this center is determined by the suspension geometry.
an imaginary point in space, look at it as the virtual hinge your car hinges around when its chassis rolls in a corner
A vehicles center of gravity, which is dependent on many variables such as weight of vehicle, ride height, suspension dampening, swaybar rigidity, unsprung weight, etc.