I am using a jQuery based WordPress Twitter widget and receive the error ReferenceError: _ is not defined.

Am not sure how to declare the variable _.

Here is the widget:

<script type=text/javascript>

    <!--//--><![CDATA[//><!--



        function twitterCallback2(twitters) {



            var statusHTML = [];

            for (var i=0; i<twitters.length; i++){

                var username = twitters[i].user.screen_name;

                var status = twitters[i].text.replace(/((https?|s?ftp|ssh)://[^s<>]*[^.,;'>:s<>)]!])/g, function(url) {

                    return '<a href='+url+'>'+url+'</a>';

                }).replace(/B@([_a-z0-9]+)/ig, function(reply) {

                    return  reply.charAt(0)+'<a href=http://twitter.com/'+reply.substring(1)+'>'+reply.substring(1)+'</a>';

                });

                statusHTML.push( '

                <li class=tweet>

                    <span class=content>'+status+'

                    <a style=font-size:85% class=time href=http://twitter.com/'+username+'/statuses/'+twitters[i].id_str+'>('+relative_time(twitters[i].created_at)+')</a></span>

                <div class=clearfix></div></li>' );

          }

          document.getElementById('twitter_update_list_<?php echo $unique_id; ?>').innerHTML = statusHTML.join('');



          var template = '

            <span class=author>

                <img src=<%= user.profile_image_url %>>&nbsp;

                <a class=username href=http://twitter.com/<%= user.screen_name %>>

                    <strong><%= user.screen_name %></strong>

                </a>

            </span>';

          jQuery( _.template( template, { user: twitters[0].user } )).insertAfter('.bizsteam_twitter ul');

        }



        function relative_time(time_value) {

          var values = time_value.split(   );

          time_value = values[1] +   + values[2] + ,  + values[5] +   + values[3];

          var parsed_date = Date.parse(time_value);

          var relative_to = (arguments.length > 1) ? arguments[1] : new Date();

          var delta = parseInt((relative_to.getTime() - parsed_date) / 1000);

          delta = delta + (relative_to.getTimezoneOffset() * 60);



          if (delta < 60) {

            return 'less than a minute ago';

          } else if(delta < 120) {

            return 'about a minute ago';

          } else if(delta < (60*60)) {

            return (parseInt(delta / 60)).toString() + ' minutes ago';

          } else if(delta < (120*60)) {

            return 'about an hour ago';

          } else if(delta < (24*60*60)) {

            return 'about ' + (parseInt(delta / 3600)).toString() + ' hours ago';

          } else if(delta < (48*60*60)) {

            return '1 day ago';

          } else {

            return (parseInt(delta / 86400)).toString() + ' days ago';

          }

        }

    //-->!]]>



    </script>

    <?php

        if($exclude_replies != ''){ $exclude_replies_str = '&amp;exclude_replies='.$exclude_replies; } else { $exclude_replies_str = ''; }

    ?>

    <script type=text/javascript src=http://api.twitter.com/1/statuses/user_timeline/<?php echo $twitter_username; ?>.json?callback=twitterCallback2&amp;count=<?php echo $twitter_count; ?>&amp;include_rts=t<?php echo $exclude_replies_str; ?>></script>

Firebug states that the line of code with the error is:

jQuery( _.template( template, { user: twitters[0].user } )).insertAfter('.bizsteam_twitter ul');

Any help would be greatly appreciated