In an algebraic expression or an equation, a letter other than the variable for which we can set the numerical value at will.

A parameter is one of the variable elements that figures in an algebraic expression or in a relation (equation, function, etc.) and for which we are interested in the characteristics that are connected to them.

### Examples

- In the relation that defines a second-degree polynomial function of variable
*x*:*f*(*x*) = a(b(*x*− h))² + k, the letters*h*and*k*are the parameters that characterize a horizontal translation and a vertical translation of the vertex of the graph, respectively. The letters a and b are also parameters that intervene in the appearance of the graph of the function. - A family of parallel lines can be expressed by the equation
*y*= m*x*+ b. If m is constant, like for example in*y*= 2*x*+ b, then this equation defines the set of parallel lines for which the slope is equal to 2. The parameter b represents the y-intercept of each line in this family.