The probability that an observation belongs to a probability distribution with parameters θ, considered as a function of the parameters rather than of the observation.
The method of maximum likelihood, originated by R. A. Fisher, estimates parameters in statistical models by maximizing the likelihood of observing the data with respect to the parameters of the model. The values taken by the parameters at the maximum are known as maximum likelihood estimates. This method is computationally equivalent to the method of least squares when the distribution of the observations about their theoretical means is the normal distribution.