I just added a few paragraphs about the three types of URL's I know about in Joomla, but I am pretty new. It needs confirmation.
More clarity was needed because this page titled about Search Engine Friendly URLS, but most folks will want SEF URLs that are also Pretty URLs rewritten by Apache mod_rewrite.
Merely SEF URLs can be very ugly and cause lots of frustration and lost business, besides making entry of Joomla URLs a hassle.
I posted on the forum about SEF URL's not working, but after several people said I already had SEF URL's I researched what mod_rewrite is about. It was really Pretty SEF URL's I wanted. I suspect my hosting support didn't correctly install Apache mod_rewrite.
I removed some incorrect information that stated URL's need a '.html' at the end to be found by search engines. This is patently false, so I'm not sure how it got here, or why it's survived so long. File extensions have nothing to do with indexability - and they're meaningless to an end-user. It's trivial to have all your PHP scripts be accessible via '.py' or '.asp' if you want, and search engine vendors know this. I'd be extremely surprised if any modern search engines apply any weight at all to extensions.
I suspect not having '.html' on your URLs at all would be the best - as you increase keyword density in the URL string (which search engines do weigh). KingJackaL 23:59, 15 March 2011 (UTC)
Added a couple of links for trouble shooting Topazgb