So like imgur or youtube for example.
Both have the url blahblahblah.com/filename.(something) and you can see that particular file as it is located there.
Subdomain may be the incorrect name for something like that.
I want to create a website where users can create those extensions.
So users can create files on the server.
What would this be called.
I am just looking for keywords to google search.
It’s usually referred to as a Content Delivery Network or CDN. There are many examples of third party CDN’s, such as Akamai or Cachefly. Huge corporations like Google have the resources to create their own and still get the same efficiency advantage.
The advantage to using a CDN is that the web servers are optimized for delivery of static content such as images, CSS, JavaScript, or downloadable content. They take advantage of robust caching schemes to avoid files being downloaded by a browser on each visit. Some third party solutions, especially Akamai, also have the added advantage of having servers within one hop of almost everyone on the planet.
A YouTube example looks like this…
More about Content Delivery Networks.