degrees of freedom
The degrees of freedom is the minimum number of independent variables in a system whose values must be specified in order to define the system. The number of degrees of freedom equals the number of variables less the number of independent relations between them (constraints). Thus Ohm's law provides one relation between three variables and there are two degrees of freedom: if the resistance of wire and the current through it are specified, both degrees of freedom have been used, and the voltage across the wire is fixed. In statistics, for a sample of n members, the distribution has (n – m) degrees of freedom where there are m constraints on the distribution.