What's the Difference Between an Argument and a Parameter?

Parameter is variable in the declaration of function.

Argument is the actual value of this variable that gets passed to function.

Simple:

• PARAMETER → PLACEHOLDER (This means a placeholder belongs to the function naming and be used in the function body)
• ARGUMENT → ACTUAL VALUE (This means an actual value which is passed by the function calling)

Parameter is variable in the declaration of function.

Argument is the actual value of this variable that gets passed to function.

There is already a Wikipedia entry on the subject (see Parameter) that defines and distinguishes the terms parameter and argument. In short, a parameter is part of the function/procedure/method signature and an argument is the actual value supplied at run-time and/or call-site for the parameter.

The Wikipedia article also states that the two terms are often used synonymously (especially when reasoning about code informally):

Although parameters are also commonly referred to as arguments, arguments are more properly thought of as the actual values or references assigned to the parameter variables when the subroutine is called at runtime.

Given the following example function in C that adds two integers, x and y would be referred to as its parameters:

int add(int x, int y) {
    return x + y;
}

At a call-site using add, such as the example shown below, 123 and 456 would be referred to as the arguments of the call.

int result = add(123, 456);

Also, some language specifications (or formal documentation) choose to use parameter or argument exclusively and use adjectives like formal and actual instead to disambiguate between the two cases. For example, C/C++ documentation often refers to function parameters as formal arguments and function call arguments as actual arguments. For an example, see “Formal and Actual Arguments” in the Visual C++ Language Reference.

A parameter is something you have to fill in when you call a function. What you put in it is the argument.

Simply set: the argument goes into the parameter, an argument is the value of the parameter.

A bit more info on: (computer_science)#Parameters_and_arguments

The use of the terms parameters and arguments have been misused somewhat among programmers and even authors. When dealing with methods, the term parameter is used to identify the placeholders in the method signature, whereas the term arguments are the actual values that you pass in to the method.

MCSD Cerfification Toolkit (Exam 70-483) Programming in C#, 1st edition, Wrox, 2013

Real-world case scenario

// Define a method with two parameters
int Sum(int num1, int num2)
{
   return num1 + num2;
}

// Call the method using two arguments
var ret = Sum(2, 3);

Let's say you're an airline. You build an airplane. You install seats in it. Then, you fill the plane up with passengers and send it somewhere. The passengers disembark. Next day, you re-use the same plane, and same seats, but with different passengers this time.

The plane is your function.

The parameters are the seats.

The arguments are the passengers that go in those seats.

function fly(seat1, seat2) {
    seat1.sayMyName();
    // Estraven
    seat2.sayMyName();

    etc.
}

var passenger1 = "Estraven";
var passenger2 = "Genly Ai";

fly(passenger1, passenger2); 

Generally speaking, the terms parameter and argument are used interchangeably to mean information that is passed into a function.

Yet, from a function's perspective:

• A parameter is the variable listed inside the parentheses in the function definition.
• An argument is the value that is sent to the function when it is called.

Always Remember that:
Arguments are passed while parameters are received.

In editing, I'm often put off at how people forget: structure languages are based on natural languages.

In English

A "parameter" is a placeholder. They set the response format, in spoken language. By definition, it's party to the call, limiting the response.

An "argument" is a position that is being considered. You argue your opinion: you consider an argument.