In a URL, what is the part after a hash sign called?

In a URL, what is the part after a hash sign called? The part after a hash sign is called the fragment identifier, or more precisely the URI fragment.

In a URL such as https://example.com/page#section, the hash mark introduces the fragment. In HTML, the fragment commonly matches an element’s id and tells the browser to scroll to that section. This is why headings and table-of-contents links can have stable deep links.

The fragment is handled by the client rather than sent to the web server in a normal HTTP request. That differs from a query string, which follows a question mark and is generally included in the request sent to the server. A port number belongs to the authority portion and follows a colon, while the domain name identifies the host.

Fragments can do more than select headings. Modern web applications use them for client-side state, and formats such as PDFs and media files may define their own fragment meanings. Strictly speaking, the # separator is not part of the fragment itself.