The number of data entries free to vary when their total is fixed.
In defining the properties of a statistical sample, the number of independent observations in a quantity. For example, if a sample contains a total of 10 children who are being classified by hair color (brown, black, or blond) and it is known that four of the children have blond hair, then there are two degrees of freedom. If, at the beginning of the investigation, the hair color of all the subjects is unknown, there are three degrees of freedom.