HTML is the main programming language used for publishing World Wide Web sites. The name stands for HyperText Markup Language and it is based on SGML or Standard Generalized Markup Language. SGML is a language that defines other markup languages such as HTML.
HTML is meant to be used for building web page's structure, while styling of the same is to be defined by another language called CSS (Cascade Style Sheets) which can be added internally or externally to the web page.
HTML elements are omitted by tags which usually come in pairs, let say a paragraph element starts with opening tag <p> and ends with closing tag </p>. This rule changes in case of having an empty element, such as a line break <br>. In that case the closing tag is skipped. XHTML 1.0 suggests to use <br /> rather then <br> tag.
HTML code in a plain text editor: