What is the difference between an argument and a parameter variable?

A parameter variable is a variable that is declared in the function signature. It represents a placeholder for a value that will be passed to the function when it is called. It can be thought of as a way to define an input value for the function.

An argument is the value that is provided to a function when it is called. It is passed to the function during the function call, and it must match the type specified by the parameter variable in the function signature. It can be thought of as the actual value that is used as input in the function call.

Let's consider a simple function to add two numbers: ```python def add_numbers(a, b): return a + b ``` In this function, `a` and `b` are parameter variables. They are declared in the function signature and represent the placeholders for the input values. Now, let's say we want to use this function to add 5 and 7. We would call the function like this: ```python result = add_numbers(5, 7) ``` In this case, `5` and `7` are the arguments. They are the actual values being passed to the function during the function call. These values replace the parameter variables `a` and `b` in the function, and the function returns the sum of these numbers, `12`. In summary, a parameter variable is a placeholder for a value in a function signature, while an argument is the actual value provided to the function when it is called.