Tagging is a way to identify posts / photos / events / albums / etc. with keywords that you can search by and cross-reference. Technorati has a good introduction to tags. Flickr uses tags as well. Now this site uses tags, of which the top 500 can be found on my tag page. You can also check for tags by using the following url: http://eecue.com/tags/[tagname]. Right now the tags are somewhat one-way (you can only see tags on the tag page... eventually each item will have a list of tags that it belongs to).