From the structural point of view, the limit load is a load that should occur only once per the aircraft lifetime.
I could only find one place that makes that statement, on Wiki.
You may take an aircraft to its limit load as often as you wish on any flight. Of course it may be detrimental in terms of fatigue life, as per my initial post. Ultimate load is the limit load multiplied by a safety factor - 150% in FAR aircraft ie an aerobatic aircraft is required to have limit load of at least +6, making the ultimate load +9. The structure in FAR certification must be able to withstand the ultimate load for at least three seconds prior to failure.