degree of freedom

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Statistics Any of the unrestricted, independent random variables that constitute a statistic.
• noun Any of the minimum number of coordinates required to specify completely the motion of a mechanical system.
• noun Any of the independent thermodynamic variables, such as pressure, temperature, or composition, required to specify a system with a given number of phases and components.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics Any of the coordinates, a minimum number of which are needed to specify the motion of a mechanical system
• noun physics Any of the independent variables required to specify the thermodynamic state of a system containing components and phases
• noun mathematics Any unrestricted variable in a frequency distribution

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (statistics) an unrestricted variable in a frequency distribution
• noun one of the minimum number of parameters needed to describe the state of a physical system