Framesets were deprecated in HTML 4 -- deprecated means "made obsolete" -- and you needed to use a special doctype in order to use them. That is to say that the W3C (the World Wide Web Consortium, which is the standards body responsible for the HTML recommendations) have been telling people for 13 years (since 1998) that framesets were going away, which is plenty of time to have found another way to do things.
The IFRAME element is supported in HTML 5 if you really feel the need to frame. Individual, separately bookmarkable pages are preferable for informational sites; dynamic HTML based upon AJAX/AJAJ or WebSockets is the preferred method for web applications. Framesets are bad from usability and accessibility standpoints, and there has been no good excuse for using them for many years.