1/ The section of the HTML document, defined with the head element, that contains elements pertaining to the document that are not part of the rendered content.

Root element

Metadata

Document head

Element

2/ Marking up a document in a way that provides the most meaningful description of the content and its function.

Validating

Semantic markup

Document head

HTML

3/A font in which all the characters have the same width.

Monospace font

Simple font

Sans serif font

Monotype font

4/ Code at the beginning of an HTML document that tells the browser what version of HTML the document is written in.

Document head

HTML

Title

DOCTYPE