Two Kinds of Keywords
http://www.webpagecontent.com/arc_archive/168/5/

McAlpine, Rachel
Quality Web Content
2005

Abstract:

I have long wondered why government web sites all over the world tend to use metadata of several different types jumbled together and overlapping. For example, pages with two description metatags or two or three title tags are common. I suspect that most of the replication and confusion has developed for historical reasons.