Although most webmasters today do not build sites with frames, many sites five and ten years ago were built with frames.  The idea was to allow one part of a site to change while the rest retains its look.  Although this was certainly a breakthrough for making web design more efficient and user friendly, the effect with search engines is very negative.

Search engines do not see the page the same way we do.  A site with frames would appear as one page to us, would appear as multiple pages to the search engine.  This means that as the search engine crawls your site, it is logging pages that have no links to other parts of your site.  Therefore when people come to your site from search engines, they end up on a page that is very confusing - and they soon leave.

There are many other technical reasons to avoid frames, but the bottom line is that if you want to have a competitive site, you need to make sure you are not using frames.  By updating your site, search engines will be able to read your site better and begin to send you more free traffic.