http://www.vbseo.com
It's Search Engine Optimization.
The one that is being used it a paid-for version. There are cheaper and free alternatives, but the bottom line is that what these modifications do is rewrite your links (for example instead of seeing xxxxxx.php, you may see xxx.html) or something similar like what you see on the website you got this from. Its most relevant feature is to drive more people to your site as search engines index .htm(l) [static] pages over .php [dynamic] pages. I'm not very familiar with this as I've not used it. But this should give you a rough idea. If someone else can better clarify this, feel free.