My understanding is that "compliance" might mean that some allowable movement is allowed to account for differeing arcs of movement from unequal length control arms.
If two different arcs are travelled while somehow being paired together, a solid connection would result in a bind, limiting total travel. Using a softer bushing would allow greater travel before binding.
When a suspension is designed, it is designed in a steady-state, with no movement of locations other than what is explicitly intended. In this state, the control arm, for instance, will move in the Z direction only [up and down]. However, when it is installed on the vehicle with rubber bushings, it will distort as it is loaded and will no longer travel only in Z.
That difference is a way to describe "compliance". Movement that is unintentional and is usually undesirable.
