DNS-Study Guide doubt(PTS prerequisites)

Hi,

This image is from DNS section.
My doubt is regarding host part.
I am not understanding how www become host.
for example let the url be
www. blog. example. com
TLD will be “.com”
Domain name will be “example”
First Subdomain will be “blog”
Second Subdomain will be “www” right.
Shouldn’t the Host be “www.blog.example.com” ?
Referred this: web services - Parts of a URL: host, port, path - Stack Overflow

Thank you