This is the URL of the Superfeedr Default PubSubhubbub Hub. This hub can only be accessed by Superfeedr Subscribers.
PubSubHubbub is an open protocol for distributed Publish/Subscribe communication on the internet.
The main purpose is to provide near-instant notifications of change updates in feeds, whether they are RSS or Atom. Superfeedr will always find the best way to identify updates in a feed and will send them to your application, so you don't have to poll.
Read this PubSubhubbub introduction if you want to get started.