Use of undefined constant comment

Hi!
I’ve just installed the Lovecraft theme, and I get this message just beneath my post and just above the comments:
Notice: Use of undefined constant comment – assumed ‘comment’ in /customers/1/5/e/pilaris.net/httpd.www/blogg/wp-content/themes/lovecraft/comments.php on line 15 14 Notice: Use of undefined constant comment – assumed ‘comment’ in /customers/1/5/e/pilaris.net/httpd.www/blogg/wp-content/themes/lovecraft/comments.php on line 16 Comments
What does it mean and what can I do to remove it?
Thank you!