In mathematics: a value that is more "built in" to a function. It is similar to a variable, but stays fixed while we use the function.
Example: in this function for the height of a tree the "20" is a parameter:
h(year) = 20 × year
We can change the parameter!
Example: A different tree's growth rate is 30 cm per year, so its function is h(year) = 30 × year
We could even make it more general by writing
h(age, rate) = rate × age
In software: it is the name given to the values that are passed in to a function.
Example: in this function, "val" is a parameter:
function double(val) {
return val*2
}
When we call the function such as double(7), then "7" is called an argument.