php - What does -> mean in the context of this function call?

$title = l(
    $comment->subject,
    comment_node_url(),
    array('fragment' => "comment-$comment->cid")
  );

Ok, so $title is the l() function, and from what I'm reading, I am passing the $comment->subject argument to l() - is that correct?

What does $comment->subject mean? I'm looking all over and not understanding what it means. Is it an operator of some sort?

Sorry if this is a simple question - I just can't find the answer anywhere.