A tag is a word or short phrase that describes something. Tags are usually directly attached to the item they describe.
Tags are a particular kind of metadata (information about other information) that is unique because it is completely under the user’s control. A tag may describe any attribute of the item it is attached to, allowing more flexibility than other classification systems.
Some programs refer to tags as keywords or categories. Although “keyword” and “tag” are almost always interchangeable, “category” is sometimes used to mean something different from “tag”. It just depends on the program.
In Mac OS X tags are often depicted with a light blue background and a rounded blue border (similar to the addresses when you are responding to an email in Mail.app).
The benefit of using tags, or software that includes tags, is that tags are extremely flexible. An item can be given any number of tags, and they may refer to any aspect of the item. For instance, I might have a photo that I tag with “france” (the location of the photo), “summer vacation” (the trip), “girlfriend” (who is in the photo), and “blurry” (how the photo looks). Then when I try to find the photo later, I can search for any of those tags (or any combination) rather than having to remember when the photo was taken or what folder I stored it in.
Tags also permit more powerful saved searches, a topic I will cover in a future article.
This isn’t to say there are no downsides to tags, of course, but I will discuss them in a future article.
Although tagging took off in online software (such as del.icio.us and Flickr), tags have been integrated into all sorts of desktop software. Tagging bookmarks, tagging files and documents, and tagging images are some of the more popular uses for tags, but there is also financial software, writing software, and many others that also use tags.
For a mostly-complete list of Mac OS X software that uses tags, please see the software list.
You should now have at least some idea of what tags are, but knowing what they are doesn’t necessarily help any with how to use them. Over the next several weeks, I will be writing a series of articles looking at different kinds of tagging systems and how to use them. Check back!
If you’re interested in general guidelines for tagging, try the “Tagging guidelines” series: Best tagging practices, A singular question, Replacing spaces, More to life than tags, and The what (more articles forthcoming!).