PHP Error [8]

Undefined index: id (/home/tkservis/public_html/app/modules/articles/articles.php:22)

#0 /home/tkservis/public_html/core/Router.php(86): Page->__construct()
#1 /home/tkservis/public_html/core/App.php(19): Router->start()
#2 /home/tkservis/public_html/index.php(18): App->start()