Hostprovider is anything that is able to produce a host.
For example, you can create a GCE hostprovider using a Google Cloud account. After you place credentials to the created GCE hostprovider, it allows you to create a host in GCE. You also can create several hosts having the same hostprovider and, consequently, the same credentials.
You can see the list of hostproviders at the HOSTPROVIDERS tab.