A parameter is a user-defined variable, which is used to store numbers and expressions.
For example, parameters pi and radius are defined as follows:
pi = 3.141592654
radius = 56
A third parameter circumference can be defined using parameters pi and radius:
circumference = 2*pi*radius
When you update the radius, circumference is automatically updated.
param_name=expression
where param_name is the name of the parameter and expression is an expression representing the numeric value of the parameter.