HTML stands for HYPERTEXT MARKUP LANGUAGE. It is a standardized language for all web pages. It tells the browser how the content will be displayed. i.e. Whether the content is in list, bold, italic, which font, location etc.
As discussed in HTML HISTORY, the basic concept of HTML is to separate content from its presentation. Let us understand this point with the help of an example.
When we write something, we have several different kinds of components in writing. For example, Title, Headings, Paragraphs, Bold, Italic, Underline and so on. The components listed above are the attributes of the text written. It has nothing to do with the content of the write up. So , in HTML it becomes a separate issue to PRESENT the content from the WRITING of the content.
The Author has to just write and generate the content and the PRESENTER can arrange it to make it more useful by setting the titles, heading etc. as per his choice.