HTML (HyperText Markup Language) is a markup language used to create webpages. It is the most commonly used language on the internet and is used to define the structure, content and design of a webpage. HTML documents are composed of elements that are used to provide structure, content and layout for the webpage.

An HTML document begins with a document type declaration, which identifies the version of HTML used in the document. This is followed by the HTML element, which contains the root element and all other elements in the document. The root element is the one element that is the “parent” of all other elements on the page.

The elements within an HTML document can be classified into two main types: structural elements and content elements. Structural elements are responsible for the structure of the page and provide the framework for the content elements. These include tags such as <head>, <body>, <title>, <meta> and <link>. Content elements provide the actual content of the page, such as text, images, videos and audio. They include tags such as <p>, <h1>, <img>, <video> and <audio>.

HTML documents also contain various attributes that provide additional information about the elements. Attributes are used to define the behavior of elements and provide additional information about the content. Attributes include things like the id, class, href, src and style.

Finally, HTML documents are also made up of comments, which are used to provide additional information or notes about the code. Comments are not visible in the browser, but can be useful for providing helpful notes to developers or other users who may be viewing the code.

HTML documents are used in webpages all over the world and are an essential part of the internet. They are used by developers to create websites, webpages and web applications. HTML documents are easy to create and understand, and are an important part of the web development process.