Probability is potential which can be confidently measured or calculated on a scale from 0 to 1 (or 0% to 100%) absence to presence.
Probability represents confidence of measurement or calculation, in contrast to confidence of belief. For example, an agent can be extremely confident that a six-sided die role has a 1/6 chance of resulting in "3", and be quite unconfident that "3" will be the (rather unlikely) result.
(tangential extended draft notes below)
Probability may represent variability which seems practically arbitrary or highly predictable at any specific hierarchical level.
For example, the probability of a getting a result of "1" on a six-sided die roll is almost exactly 1/6 or 16.7%, and that variability seems practically arbitrary. By contrast, the probability of an arbitrarily selected student getting an "A" on a specific test may be roughly 1/4 or 25%, and that variability may seem to be consistently related to specific factors such as requirements.
Practicalities and impracticalities of calculating probability: People often incorporate probability perceptions and risk assessment into their decision processes. Usually it's entirely informal, and for good reason.
For instance, I may quite roughly intuit that there's roughly a '50/50' chance that I'll fall to my death if climb along the edge of a certain cliff. In all likelihood, it would be an extremely unrealistic waste of time to ambitiously try to calculate a specific probability of fatality, even if I applied a broad standard deviation to the number I generated. I'm probably just going to stay away from that cliff edge.
It's only rational to calculate probabilities when our intuitions, and/or qualitative analyses, fail to clearly suggest which decisions or actions are preferable, and the cost of calculation seems to be lower than the cost of not calculating. -- The cost of calculating is much more likely to be justified during the development of standardized recipes or models of organization, than it would be in dealing with relatively specific or unique situations.