1. When referring to HTML, XML, or other markup languages a tag is an element inserted into a document or file that changes the look of content or performs an action. As seen in the HTML tag example, an HTML element has an open tag that contains the name and any attributes and a close tag that contains a forward slash and the name of the tag being closed.
Each tag is contained within a less than and greater than angle brackets and everything between the opening and closing tag is displayed or affected by the tag. In the above example, the <a> tag is creating a link called "Computer Hope" that is pointing to the hope.html file.
For tags that do not have a closing tag like the <img> tag, it is best practice to end the tag with a forward slash, as shown below.
2. A tag is a short (usually one word) description of an HTML object or link. These tags are typically placed in a tag cloud also known as weighted lists to show the most popular tags on a website or blog, which allows visitors to find information that may be of interest.
In the picture is an example of a tag cloud of the text contained on this page that was generated using the TagCrowd website.
3. A tag is a memory that acts as an index for L2 (Level 2) Cache.