A "hard link" is a direct link, rather than a link to a script that re-directs you. Think of it this way:
<a href="http://www.google.com">google</a>
This is a hardlink.
<a href="http://www.mysite.com/redirect/out.php?destination=google.com">google</a>
This is not a hardlink.
People like hardlinks because (generally speaking) search engines look at the number of pages that link to your page when determining where your page appears in the search rankings.
Hope that helps!
