Difference between head and header?

Answer 1

Head sits outside Body, containing code not rendered on the page by the browser, like <title> to name the tab. Header is inside Body, and it's contents are viewable in browser.

Answer 2

Think of it this way:

Head describes the page itself - the title on the address bar, the scripts, the metadata, the language, the CSS, etc. The thought process behind this display. It is not shown.

Body is what you can see on display in the browser page:
1. Header is the headline, topic of this page. Close by, you have navigation elements.
2. Articles, sections are subparts of the page.
3. Footer is the copyright section, with mainly links to other pages, etc.