Many functions give different results depending on the parameters that are supplied. For example, before you can carry out the mathematical function of rounding a number, you need to supply a number. This number is the parameter.
The number 5.879 can be rounded by supplying it as a parameter to the round() function: round(5.879)
A function may take more than one parameter. For instance, the pow() function takes two parameters, x and y for example, so that xy can be calculated: pow(3,2)