Va is the speed at which the pilot can deflect the controls to the maximum inputs and not exceed the G limits of the aircraft.
I don't think that's exactly right. I think it's the max speed at which the sudden and full deflection of any *single* control is sure not to cause structural damage.
I believe in pratical circumstances, the most limiting control input is full up-elevator, which is why Va is usually set at the square-root of the g-limit times VS0, and why Va decreases as the weight goes down.
I do recall that if at Va you input full up elevator
and full aileron you could well damage the airframe.