HTML stands for Hypertext Markup Language, and it is the most widely used language for creating Web pages.
The declaration tag is used by the web browser to understand the version of the HTML used in the document. Current version of HTML is 5 and it makes use of the following declaration-
<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
</head>
<body>
<h1>This is a Heading</h1> <p>This is a paragraph.</p>
</body>
</html>