When there is 30V across the collector and base (which is the breakdown voltage, so there had better be no more than 30V in any circuit!), and no current following out of the emitter, (for example, if someone's connected a 30V battery and meter across the collector and base), at most 1uA flows between the collector and base.
Ideally there should be none at all (the transistor is off), but at the maximum voltage for the CE junction, a little leaks through, but no more than this even at this extreme voltage.
A similar analysis holds for the emitter-base junction with the other figure.
I assume this is considered a useful measurement because the reader is expected to assume there will be the same or less leakage at lower voltages.
Think of it like this, if you have a water tap it will have a maximum pressure it can handle. That will be in its "datasheet". At exactly that maximum pressure, even if the tap is off, a little may leak through the tap. That's what this figure represents.