The list of identifiers used in a function call is called actual parameter(s) whereas the list of parameters used in the function definition is called formal parameter(s).
Actual parameter may be value / variable or expression.
Formal parameter is an identifier.
Example:
def area(side): # line 1
return side*side;
print(area(5)) # line 2
In line 1, side is the formal parameter and in line 2, while invoking area() function, the value 5 is the actual parameter.
A formal parameter, i.e. a parameter, is in the function definition. An actual parameter, i.e. an argument, is in a function call.
