Many websites make use of frames on their web pages. In some cases, more than two frames would be used on a single web page. The reason why most websites use frames is because each frame's content has a different source. A master page known as "Frameset" controls the process of clubbing content from different sources into a single web page. Such frames make it easier for webmasters to club multiple sources into a single web page. This, however, has a huge disadvantage when it comes to Search Engines.
Some of the older Search Engines cannot read content from frames. This only crawl through the frameset instead of all the web pages. Consequently, web pages with multiple frames are ignored by the spider.
There are certain tags known as "NOFRAMES" (Information ignored by frames capable browser) that can be inserted in the HTML of these web pages. Spiders can read information within the NOFRAMES tags. Thus, Search Engines only see the Frameset. Moreover, there cannot be any links to other web pages in the NOFRAMES blocks. That means the search engines won't crawl past the frameset, thus ignoring all the content-rich web pages that are controlled by the frameset.
Hence, it is always advisable to have web pages without frames as these could easily make your website invisible to Search Engines.