HTML tags are used to mark up content and are denoted by tag names surrounded by less than and greater than brackets. Different tags have different names, such as body, paragraph, and image tags. HTML tags typically consist of an opening and closing tag, except for void tags which cannot have any content inside them. Void tags do not require a closing tag and examples include the image tag. Self-closing tags, a leftover from XHTML, may also be seen in HTML. These tags do not have a closing tag and were part of a previous version of HTML called XHTML.