Tags can be in the form of words, images or marks. They help search engines identify the content of pages online and, using that information, produce the best results for a given search. Tagging was popularized by websites associated with Web 2.0.

Tags are useful not only for the one who employs them but also for other website users. Websites that use the tag feature usually display them as a collection of tags, which are known as tag clouds. This allows users to navigate more effectively by clicking on the tag that interests them within the cloud, thereby displaying all the content with that particular tag.

There are two different types of tags:

• Triple Tag: Uses a special type of syntax to define extra semantic information about the tag. These tags consist of three parts: a namespace, a predicate and a value.
• Hashtag: Hashtags include the use of the hash symbol (#) with one or more words following it. This type of tagging is often used by microblogging platforms like Twitter.
  

New tags can be applied to an item as easily as older tags and they are intended to help classify items in a way that is useful to users. In some cases, users can create the tags of their choice. However, this option sometimes results in metadata that includes homonyms and synonyms that may lead to inappropriate search information about a subject.