The probability of an event 
is a measure between 0 and 1
of whether the event is likely to happen.
The word ``probability'' is derived from the word
``probable'' that comes from the Latin word prob
bilis
meaning provable, which is rather paradoxical since only when the
the probability is exactly one or zero can anything be definitely proved!
The different ways that can be used to define the concept of
probability are briefly described below: