How to do fix the global symbol requires explicit package using Perl?

Global symbol "%href_to_what" requires explicit package

<pre>while (my $line=<$fh>) {
    chomp $line;
    for($line)
    {
    s/\&//g;
    s/[\\\_\@\_]//g;
    s/COMMENT//g;
    }
    my @data = split /:/, $line;
    my $class = $data[0] ? 'normal' : 'bold';
    print $fh_out qq[<tr class="$class">];
    my $ct=0; 
    for my $word(@data){ 
      $ct++; 
      print $fh_out '<td>';
      if ($ct==1){ 
          print $fh_out '<a href="'
                       .$href_to_what{$word}
                       .'">'; 
          } 

      print $fh_out $word; 
      if ($ct==1){ 
          print $fh_out '</a>';
          } 
      print $fh_out '</td>'; 
      } 
    print $fh_out "</tr>\n";
    }