HTML stands for Hypertext Markup Language. It is a standard markup language used for creating web pages and applications. The term "markup" refers to the process of adding tags to text in order to define its structure and presentation. HTML uses tags to define elements such as headings, paragraphs, images, links, and more. These tags are then interpreted by web browsers to display the content in a formatted and structured manner. Therefore, the correct answer is "Hypertext Mark Up Language".