Roles

The Third-Party Application: "Client"

The client is the application that is attempting to get access to the user's account. It needs to get permission from the user before it can do so.

The API: "Resource Server"

The resource server is the API server used to access the user's information.

The Authorization Server

This is the server that presents the interface where the user approves or denies the request. In smaller implementations, this may be the same server as the API server, but larger scale deployments will often build this as a separate component.

The User: "Resource Owner"

The resource owner is the person who is giving access to some portion of their account.