The name tag system refers to any of several methods for marking items using technology. The three main uses of a tag system in twenty-first century technology are to connect metadata to multimedia, to connect barcoded images to information and entertainment that someone has chosen to link to them, and to signal to web browsers how to render content on web pages. Each of these three systems is completely separate and works in a completely different way.
The metadata tag system for multimedia, such as audio and video files, contains information about the contents of the file, as well as data such as the artist, album, title, track number, scene, etc., as relevant to the type of media being tagged. There are several standards for tag format including ID3v1 and ID3v2, as well as APEv2, Vorbis comments, MPR (the iTunes® metadata tag) and Windows Media, but in every case, the metadata in the tags is separate from the actual audio or video content of the file. Metadata tags help users to identify and organize their collections. There are also metadata tag editors, which allow tags to be edited individually or in batches and also help with file organization.
The second type of tag system is the Microsoft® Custom Tags which uses barcode images that can be turned into personal icons to connect the object on which the image appears to whatever information has been attached to it by the image owner. Individuals can make their own image and “reading” the tags is done using a mobile phone which can interpret them by taking a photo or a scan. An example is an advertising poster a restaurant has posted at a bus stop with a Microsoft® Custom Tag linking to their website reservations page. A passerby who scans the tag is taken to the website using the browser on his or her smartphone and can immediately make a reservation for a meal.
The third type of tag system is the method for showing elements in HTML. This tag system can both indicate types of objects, as well as actions, and hierarchy. For example, the heading structure of a website can be created through the HTML tag system.