What is the difference between parameter and argument in C#?

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

Below are examples of each.

// a and b are parameters

public int add(int a, int b) 
{
    return a + b;
}

// 2 and 3 are arguments (parameter values)

var sum = add(2, 3);