Logic Jquery ' ? ' and ' : '

Question

Hello, I’m a beginner in jquery, and I was looking at the documentation for Jquery Ui, Draggable and Droppable. I’m studying the demo of the site, but I don’t understand this part:

var $list = $( "ul", $trash ).length ?
  $( "ul", $trash ) :
  $( "<ul class='gallery ui-helper-reset'/>" ).appendTo( $trash );

I don’t understand the part ? after the .length and the : after the $( "ul", $trash ). This is the complete function:

function deleteImage( $item ) {

  $item.fadeOut(function() {
    var $list = $( "ul", $trash ).length ?
      $( "ul", $trash ) :
      $( "<ul class='gallery ui-helper-reset'/>" ).appendTo( $trash );

    $item.find( "a.ui-icon-trash" ).remove();
    $item.append( recycle_icon ).appendTo( $list ).fadeIn(function() {
      $item
        .animate({ width: "48px" })
        .find( "img" )
          .animate({ height: "36px" });
    });
  });
}

And this is the event that calls the function:

var $gallery = $( "#gallery" ),
      $trash = $( "#trash" );

$trash.droppable({
  accept: "#gallery > li",  
  classes: {    
    "ui-droppable-active": "ui-state-highlight"
  },
  drop: function( event, ui ) { 
    deleteImage( ui.draggable );
  }
});