What is Uncertainty?

Legal Definition
Uncertainty is a situation which involves imperfect and/or unknown information. However, "uncertainty is an unintelligible expression without a straightforward description". It arises in subtly different ways in a number of fields, including insurance, philosophy, physics, statistics, economics, finance, psychology, sociology, engineering, metrology, and information science. It applies to predictions of future events, to physical measurements that are already made, or to the unknown. Uncertainty arises in partially observable and/or stochastic environments, as well as due to ignorance and/or indolence.
-- Wikipedia
Legal Definition
Such vagueness, obscurity or confusion in any written instrument, e. g., a will, as to render it unintelligible to those who are called upon to execute or interpret it, so that no definite mcaning can be extracted from it.
-- Black's Law Dictionary
Legal Definition
That which is unknown or vague. Vide Certainty.
-- Bouviers Law Dictionary