Probability Measure
A Probability Measure is a function that assigns real-valued and countably additive measurement results between 0 and 1.
The functional flow looks like this:
Sample Space => Event Space => Probability Function => Probability Measurement
Likelihood
Likelihood is the probability that an event that has already occurred would yield a specific outcome.
Likelihood differs from probability in that it refers to past events where probability refers to the occurrence of future events.
An Example
An an example in Machine Learning is the use of a trained model to make a prediction.