Social bookmarking site del.icio.us is launching a feature today called tag descriptions - essentially a way to add an explanation of your tags.
Tagging pretty much began with del.icio.us, and became a great way for people to add labels to items without the need for creating folders - tags also meant that links from lots of users could be aggregated under one topic, without any need for interaction between the users. Flickr, YouTube and others adopted the idea for other media types.
So it's interesting to note that del.icio.us is expanding the tagging concept with tag descriptions, a feature that now appears on your tag page. The benefit, however, is mainly to other users, who can understand exactly what you mean when you use obscure words as tags. The question I have is: how many people will bother? Do you really want to be filling in even more fields?