jQuery validation error "not defined"

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When validating the jQuery I receive the followers 2 errors: "'$' was used before it was defined." & "'window' was used before it was defined." What does this mean? & how do I remove these errors? Thank you :-)

var lastScrollTop = 0;
$(window).scrollTop(0);

$(window).on('scroll', function() {
    var header = $('header');
    var content = $('content');
    var headerBg = $('.header-bg');
    var headerCnt = $('.header-content');
    var scrollTop = $(window).scrollTop();
    var dynHeaderVisible = false;
  
    if (lastScrollTop > scrollTop) {
      if (scrollTop <= 400) {
        headerBg.css("height", 0);
        headerCnt.css('color', 'white');
      } else {
        headerBg.css("height", 80);
        headerCnt.css("height", 80);
        headerCnt.css('color', 'black');
      }
    } else {
      // Down
      if (scrollTop > 350) {
        console.log ("hi");
        headerCnt.css("height", 0);
        headerBg.css("height", 0);
      }
    }
    
    lastScrollTop = scrollTop;
});

$.fn.isOnScreen = function(){
    var element = this.get(0);
    var bounds = element.getBoundingClientRect();
    return bounds.top < window.innerHeight && bounds.bottom > 0;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  width: 100%;
  margin: 0;
  list-style: none;
  text-decoration: none;
  font-size:1em;
  font-family: Helvetica Neue, Helvetica, Arial, Sans-serif;
  }
        a {
    background:transparent;
    border:none;
    letter-spacing:0.15em;
    text-transform:uppercase;
    transition: .3s color;
        transition: .3s height;
        }


header {
  display: block;
  position: fixed;
  height: 80px;
  width: 100%;
}

header ul {
  z-index: 20;
}

.header-wrapper {
  position: relative;
  width: 100%;
  height: 100%;
  background-color: transparent;
}

.header-bg,
.header-content {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  text-align: center;
}

.header-bg {
  z-index: 100;
  color: gray;
  background-color: white;
  border-bottom: 1px solid black;
  transition: .3s height;
  height: 0;
}

.header-content {
  z-index: 200;
  transition: .3s color;
  color: white;
  background-color: transparent;
  height: 80px;
  transition: .3s height;
  overflow: hidden;
  list-style: none;
}

.logo {
    position: absolute;
    left: 47%;
        color: inherit;
    display: inline-block;
    width: 15px;
    height: 15px;
    padding: 18px;
    cursor: pointer;
    font-size:.8em;
    letter-spacing:0.05em;
        transition: .3s color;
        }

content {
  display: block;
  height: 2000px;
  background-color: orange;
}

.stage {
    color: #fff;
    display: -webkit-box;
    display: -webkit-flex;
    display: -ms-flexbox;
    display: flex;
    -webkit-box-pack: center;
    -webkit-justify-content: center;
    -ms-flex-pack: center;
    justify-content: center;
    -webkit-box-align: center;
    -webkit-align-items: center;
    -ms-flex-align: center;
    align-items: center;
    height: 100vh;
    background-color: white;
        border-bottom: 1px solid black;
    font-size: 48px;
        height: 200px;
        width: 100%;
}

.stage-0 {
    background: grey;
    height: 400px;
}

<script src=     "//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<header>
  <div class="header-wrapper">
    <div class="header-bg"></div>
    <div class="header-content">
      <ul>
        <li>
        <a href="" class="logo">Logo </a>
        </li>
      </ul>
    </div>
  </div>
</header>
<content>
<div class="stage stage-0">1</div>
<div class="stage stage-2">3</div>
<div class="stage stage-4">5</div>
<div class="stage stage-6">7</div>
<div class="stage stage-8">9</div>
<div class="stage stage-10">11</div>
<div class="stage stage-12">13</div>
<div class="stage stage-14">15</div>
<div class="stage stage-16">17</div>
<div class="stage stage-18">19</div>
<div class="stage stage-20">21</div>
<div class="stage stage-22">23</div>
</content>

asked 30 secs ago

Dee

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jQuery validation error "not defined"