ReferenceError: _ is not defined
<p>I am using a jQuery based WordPress Twitter widget and receive the error "<code>ReferenceError: _ is not defined</code>".</p>

<p>Am not sure how to declare the variable "_".</p>

<p>Here is the widget:</p>

<pre><code>&lt;script type="text/javascript"&gt;
    &lt;!--//--&gt;&lt;![CDATA[//&gt;&lt;!--

        function twitterCallback2(twitters) {

            var statusHTML = [];
            for (var i=0; i&lt;twitters.length; i++){
                var username = twitters[i].user.screen_name;
                var status = twitters[i].text.replace(/((https?|s?ftp|ssh)\:\/\/[^"\s\&lt;\&gt;]*[^.,;'"&gt;\:\s\&lt;\&gt;\)\]\!])/g, function(url) {
                    return '&lt;a href="'+url+'"&gt;'+url+'&lt;/a&gt;';
                }).replace(/\B@([_a-z0-9]+)/ig, function(reply) {
                    return  reply.charAt(0)+'&lt;a href="http://twitter.com/'+reply.substring(1)+'"&gt;'+reply.substring(1)+'&lt;/a&gt;';
                });
                statusHTML.push( '\
                &lt;li class="tweet"&gt;\
                    &lt;span class="content"&gt;'+status+'\
                    &lt;a style="font-size:85%" class="time" href="http://twitter.com/'+username+'/statuses/'+twitters[i].id_str+'"&gt;('+relative_time(twitters[i].created_at)+')&lt;/a&gt;&lt;/span&gt;\
                &lt;div class="clearfix"&gt;&lt;/div&gt;&lt;/li&gt;' );
          }
          document.getElementById('twitter_update_list_&lt;?php echo $unique_id; ?&gt;').innerHTML = statusHTML.join('');

          var template = '\
            &lt;span class="author"&gt;\
                &lt;img src="&lt;%= user.profile_image_url %&gt;"&gt;&amp;nbsp;\
                &lt;a class="username" href="http://twitter.com/&lt;%= user.screen_name %&gt;"&gt;\
                    &lt;strong&gt;&lt;%= user.screen_name %&gt;&lt;/strong&gt;\
                &lt;/a&gt;\
            &lt;/span&gt;';
          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 &gt; 1) ? arguments[1] : new Date();
          var delta = parseInt((relative_to.getTime() - parsed_date) / 1000);
          delta = delta + (relative_to.getTimezoneOffset() * 60);

          if (delta &lt; 60) {
            return 'less than a minute ago';
          } else if(delta &lt; 120) {
            return 'about a minute ago';
          } else if(delta &lt; (60*60)) {
            return (parseInt(delta / 60)).toString() + ' minutes ago';
          } else if(delta &lt; (120*60)) {
            return 'about an hour ago';
          } else if(delta &lt; (24*60*60)) {
            return 'about ' + (parseInt(delta / 3600)).toString() + ' hours ago';
          } else if(delta &lt; (48*60*60)) {
            return '1 day ago';
          } else {
            return (parseInt(delta / 86400)).toString() + ' days ago';
          }
        }
    //--&gt;!]]&gt;

    &lt;/script&gt;
    &lt;?php
        if($exclude_replies != ''){ $exclude_replies_str = '&amp;amp;exclude_replies='.$exclude_replies; } else { $exclude_replies_str = ''; }
    ?&gt;
    &lt;script type="text/javascript" src="http://api.twitter.com/1/statuses/user_timeline/&lt;?php echo $twitter_username; ?&gt;.json?callback=twitterCallback2&amp;amp;count=&lt;?php echo $twitter_count; ?&gt;&amp;amp;include_rts=t&lt;?php echo $exclude_replies_str; ?&gt;"&gt;&lt;/script&gt;
</code></pre>

<p>Firebug states that the line of code with the error is:</p>

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

<p>Any help would be greatly appreciated</p>
