Tagging has become a popular standard in Web content management. If you can enter a field of data somewhere, chances are good you can also attach tags. Tags let a user associate that data with a subject matter, much like a card catalogue in a library. When that user goes to retrieve the data, they need only remember a keyword or two to find it. All the posts on this blog, for instance, have tags to denote the topics covered. Social bookmarking sites allow users to tag their links. Photo sharing apps like Flickr do it as well. It's a helpful convenience for when you're out with a camera or in with a laptop.