What does DOCTYPE mean?

DOCTYPE mean Document Type Defination
<!Doctype> eliment does not have closing tag.
<!Doctype> is not an HTML tag.

HTML Headings

HTML headings are defined with the <h1>to <h6> tags.
<h1> tag is a longest heading tag of html
<h6> tag is a shortest heading tag of html

What is HTML?

HTML stands for Hyper Text Markup Language
HTML elements are represented by tags
It is use for create of Website

HTML Documents

All HTML documents must start with a document type declaration:<!Doctype html>
The visible part of the HTML document is between <body> and</body>
The HTML document itself begins with <html> and ends with</html>.

HTML Example:

<!Doctype html >
<html>
<head>
<title>Docoment title</title>
</head>
<body>
<h1>This is A Sample Heading </h1>
<h2>This is A Sample Heading </h2>
<h3>This is A Sample Heading </h3>
</body>
</html>