How does this Javascript work?

I've got some JS I'm attempting to deconstruct so I can add some functionality to it. First, however, I want to understand what I'm looking at. Here's what I've got:

First the JS itself:

define(['/assets/js/views/app2/custom_checkbox_and_radio.js','jquery'],function(){
    return function(){
      $('.at_filters label').click(function(){
        $(this).siblings('.checkbox').click();
      });
      $('input[name="filt"]').on('change',function(){
        if(this.value=='all'){
          if($(this).is(':checked')) $('input[name="filt"]').attr('checked', true);
          else $('input[name="filt"]').attr('checked', false);
        } else {
          $('input[name="filt"][value="all"]').attr('checked', false);
        }
        var show = [];
        var left = true;
        $('input[name="filt"]:checked').each(function(){
          show.push($(this).val());
        });
        var year = '';
        var month = '';
        $('.at_timeline_list li').each(function(){
          if($(this).hasClass('yearheader')){
            if(year && year.data('delete')) year.slideUp();
            else if(year) year.slideDown();
            year = $(this);
            year.data('delete', true);
          } else if($(this).hasClass('monthheader')){
            if(month && month.data('delete')) month.slideUp();
            else if(month) month.slideDown();
            month = $(this);
            month.data('delete', true);
          } else if($(this).hasClass('event')){
            if(show.indexOf($(this).data('type'))!=-1){
              $(this).removeClass('left').removeClass('right');
              $(this).addClass(left?'left':'right');
              left=!left;
              if($(this).css('display')!='list-item') $(this).slideDown();
              year.data('delete',false);
              month.data('delete',false);
            } else {
              if($(this).css('display')=='list-item') $(this).slideUp();
            }
          }
        });
        if(year && year.data('delete')) year.slideUp();
        else if(year) year.slideDown();
        if(month && month.data('delete')) month.slideUp();
        else if(month) month.slideDown();
      });

      //Account Search
      $('input.at_search').keypress(function(e){
        if(e.which == 13){
          $(this).siblings('.magnificon').click();
        }
      });
      $('.at_searchwrap .magnificon').click(function(){
        if(!$('.at_search').val()) return;
        pf.ajax({
          url:'/app/accounttimeline',
          data:{searchfor:$('.at_search').val()},
          type:'post',
          dataType:'json',
          success:function(res){
            if(res.success && res.body){
              if(res.loadAccount){
                pf.apps.loadApp({
                  appurl:'/app/accounttimeline',
                  postdata:{accountkey:res.loadAccount},
                  refresh:new Date()
                });
              } else pf.dialog(res.body, 'Search Results');
            } else {
              pf.dialog('There has been an issue processing your request. I apologize for the inconvenience, please try again.', 'Error');
            }
          }
        });
      });

      setupLabel();
    };
});

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Here's a screenshot of the page:


I want to break this down into several questions, just so I'm not wearing out my welcome.  What I want to do is define that which I understand and ask for confirmation on those things and then crescendo to that point where I've got a question. That said, here's the first "dilemma:"

define(['/assets/js/views/app2/custom_checkbox_and_radio.js','jquery'],function(){

I'm defining a series of variables located on the "customer_checkbox_and_radio.js" page (https://github.com/amdjs/amdjs-api/wiki/AMD). The next part says, "function." I'm thinking this is shorthand for "document.ready..." In other words, don't try to fire the function that's documented immediately following this syntax until the entire page is loaded.

The next part baffles me. I'm returning a function?

return function(){

The next body of code has this:

  $('.at_filters label').click(function(){
        $(this).siblings('.checkbox').click();
      });

What's happening here? I've got a class "at_filters label" which matches my code here:

<div class="at_searchwrap clearfix"><input class="at_search" placeholder="Search by first name, last name, or accountid."/><span class="magnificon"></span></div>
    <ul class="at_filters">
      <li>
        <span class="checkbox">
          <input type="checkbox" name="filt" value="all" checked/>
        </span><label>All</label>
      </li>
      <li>
        <span class="checkbox">
          <input type="checkbox" name="filt" value="transaction" checked/>
        </span><label>Transactions</label>
      </li>
      <li>
        <span class="checkbox">
          <input type="checkbox" name="filt" value="statement" checked/>
        </span><label>Statements</label>
      </li>
      <li>
        <span class="checkbox">
          <input type="checkbox" name="filt" value="note" checked/>
        </span><label>Notes</label>
      </li>
      <li>
        <span class="checkbox">
          <input type="checkbox" name="filt" value="comment" checked/>
        </span><label>Task Comments</label>
      </li>
	  <li>
        <span class="checkbox">
          <input type="checkbox" name="filt" value="personal_payments" checked/>
        </span><label>Personal Payments</label>
      </li>
    </ul>

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Every one of these checkboxes is tied to this function, but what is that function doing?

What do you think?