Question

why exactly is the term argument used interchangeably with the term parameter in regards to functions or methods? seems ridiculous to me and in fact undermines programming altogether, except for the fact that it works.

Answer 1

Using the terms interchangeably is incorrect.

An argument is a value passed in a function call.

A parameter is an object, local to the function, into which the argument value is copied.

For example:

void foo(int parameter) {
    /* ... */
}

/* ... */

int argument = 42;
foo(argument);

The definitive reference for this is the C standard (3.7M PDF). The words argument and parameter are defined in 3.3 and 3.15, respectively.