A vague concept which occurs all through statistics. Essentially the term means the number of independent units of the information in an easy relevant to the estimation of the parameter or calculation of a statistic. For instance, in a two-by-two contingency table with the provided set of marginal totals, only one out of the four cell frequencies is free and the table has thus a single degree of freedom. In number of cases the term corresponds to the number of parameters in the model. It is also used to refer to a parameter of the various families of distributions such as, Student's t-distribution and the F- distribution.