What are tags?

Tags are one-word descriptors that you can assign to your bookmarks on Delicious to help you organize and remember them. Tags are a little bit like keywords, but you choose them yourself and they do not form a hierarchy. You can assign as many tags to a bookmark as you like and you can always rename or delete the tags later. So, tagging can be a lot easier and more flexible than fitting your information into preconceived categories or folders.

For example, if you save an article about how to make a certain kind of cake, you can tag it with recipes sweets yogurt or whatever other tags you might use to find it again. You don’t have to rely on the designer of a system to provide you with a category for French cake recipes. You make up tags as you need them, and use the tags that make the most sense to you.

This is great for organizing and finding personal data, but it goes even further when someone else posts related content using the same tags. You begin building a collaborative repository of related information, driven by personal interests and creative organization. 

What are some examples of tagging?

You can use tags describing an article or website’s subject, location, name, category, people, places, ideas — pretty much anything you can think of. The more tags the better! (Most people end up adding two to five tags to each of their bookmarks.)

The only limitation on tags is that they must not include spaces. So if your web page is about a two-word place like “San Francisco”, you may want to tag it as sf, san-francisco, SanFrancisco, san.francisco, or whatever else makes sense to you. You don’t want to use commas, though, since a comma will be become part of the tag. You can also use tags to describe metadata about the bookmark. For example, you can use asterisks to rate bookmarks. So a tag of * might mean an OK link, *** is pretty good, and a bookmark tagged ***** is awesome. Other common tags include toread, or via:friend. Bookmarks that you want can be tagged wishlist, and ones that might not be safe to visit at work can be tagged nsfw. A tag can be anything you want.

resources: http://delicious.com/help/faq