In the mid-90s, Netscape came up with a way to display multiple webpages within a single page.
They called it frames.
After 6 months of using it on their homepage, they came to the conclusion that they were crippling for usability so stopped using them.
... and that's about all you need to know.
See also: http://allmyfaqs.net/faq.pl?Problems_with_using_frames where some of the alternatives are described.
