in mathematics, a variable for which the range of possible values identifies a collection of distinct cases in a problem. Any equation expressed in terms of parameters is a parametric equation. The general equation of a straight line in slope-intercept form, y=mx+b, in which m and b are parameters, is an example of a parametric equation. When values are assigned to the parameters, such as the slope m=2 and the y-intercept b=3, and substitution is made, the resulting equation, y=2x+3, is that of a specific straight line and is no longer parametric.

In the set of equations x=2t+1 and y=t²+2, t is called the parameter. As the parameter varies over a given domain of values, the set of solutions, or points (x,y), describes a curve in the plane. The use of parameters often enables descriptions of very simple curves for which it is difficult to write down a single equation in x and y.

In statistics, the parameter in a function is a variable whose value is sought by means of evidence from samples. The resulting assigned value is the estimate, or statistic.