Understated comment in the thread.

The very first search hit on Google is none other than Mozilla's page on ranged requests.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Guides/Ran...

Here's the leading summary from that page.

> An HTTP Range request asks the server to send parts of a resource back to a client. Range requests are useful for various clients, including media players that support random access, data tools that require only part of a large file, and download managers that let users pause and resume a download.

Here's a RFC:

https://datatracker.ietf.org/doc/html/rfc7233