What do these parts of the URL called?

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So I have 2 questions: [*]What is this part called? en.wikipedia.org, the part before the domain name.[*]I wanted to make something like that for my website, like \[code\]firstName.lastName.web\[/code\] For my personal page on my family web site. How do I do that? I know that if I just put a folder in the root folder, its treated as a /. Like so: \[code\]lastName.web/firstName.HTML\[/code\]. That's fine, but not what I wanted.