The words ‘probably’, ‘doubt’, ‘most probably’, ‘chances’, etc., used in the statements above involve an element of uncertainty.
For example, ‘probably rain’ will mean it may rain or may not rain today.
The uncertainty of ‘probably’ etc can be measured numerically by means of ‘probability’ in many cases.

Probability started with gambling, it has been used extensively in the fields of Physical Sciences, Commerce, Biological Sciences, Medical Sciences, Weather Forecasting, etc.

A trial is an action which results in one or several outcomes.

An event for an experiment is the collection of some outcomes of the experiment.