Likelihood function

In the English language, the word likelihood means the same as, or almost the same as, the word 'probability'.

In probability theory the technical term likelihood is a concept related to, but distinct from, that of probability. (Confusingly, likelihood is also used in its informal English sense in some discussions of the interpretation of mathematical probability.)

Unlike probability, which estimates the frequency of or degree of belief in unknown consequences of known causes, likelihood works backwards, from observed results to hypothetical models and parameters.

The likelihood function does not necessarily follow all the axioms of probability: for example, the integral over the likelihood density function need not sum to 1.