Real Dictionary

parameter in American English
a quantity or constant whose value varies with the circumstances of its application, as the radius line of a group of concentric circles, which varies with the circle under consideration
noun: a constant or variable term in a function that determines the specific form of the function but not its general nature, as a in f(x) = ax, where a determines only the slope of the line described by f(x)

parameter in British English
noun: one of a number of auxiliary variables in terms of which all the variables in an implicit functional relationship can be explicitly expressed