On the Web, tags are keywords that users themselves assign to content. Tags can be used in blogs, photo sharing sites like Flickr and Picasa, video sharing sites like YouTube and Vimeo, social bookmarking sites like Delicious, and microblogs like Twitter. In Twitter, a hashtag is simply a tag with a pound sign or "hash" in front of it, as in #ala10.
There is no central authority or offical set of tags, but if many users begin to use the same tag for the same topic across all Web content, the information can be aggregated to a fuller picture of participants' experiences.
One way to view the aggregate all of this content is with a site like Addict-o-matic:
- Go to http://addictomatic.com
- Enter a tag (ex: Chile or ala10)
- Click the Create button.
- Twitter "tweets",
- FriendFeed updates,
- Wordpress, Twingly, and Bloglines blog searches,
- Google, Bing, Yahoo!, and Ask.com searches,
- Digg articles,
- Flickr images,
- YouTube and Truveo videos,
- and more!