Uncaught TypeError: $(...). x is not a function

Uncaught TypeError: $(...). x is not a function

I am making my first foray into jQuery and I can't seem to solve the 'X is not a function' error.

From what I've read online,

-for most people the problems seems to be from not declaring jQuery first in the HTML document, but I definitely have it (CDN version and local fallback) before including any other JS files.

-for others it was happening because jQuery was not getting loaded for some other reason (but for me it's definitely getting loaded, I tested for it before the line of code that causes the error and it's definitely defined /loaded).

-for others it was some type of conflict between libraries, so I have tried other solutions such as using 'jQuery' instead of '$', using the noConflict statement, and enclosing the block of code in a wrapper.

I feel like I've tried everything but I'm still getting the same error.  It's probably something simple that I, as a beginner am overlooking.

From my HTML file:

  1.     <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
        <script src="../js/jquery.js"></script>

From my javascript file:
  1. $(function () {
           
                $(window).on("load resize", function () {
                    $(".fill-screen").css("height", window.innerHeight);
                });

           
                $("#video1").background ({         /*This is the line that causes the error 'background is not a function.*/
                    source: {
                    poster: XXXXX
                    video: XXXXX
                    }
                });
        });

Thanks in advance for any help.