A Docker Registry is a repository which you can upload your Docker images to, so they can be downloaded later, either by you or by your clients or users. The Docker company (the company behind Docker) has a service called Docker Hub which is essentially a hosted Docker Registry which you can upload your Docker images to, and access them later. Docker Hub has both private and public registries. A private registry can only be accessed by you, which is ideal for internal applications. A public registry can be used by anyone, which is ideal for open source applications.
Signing Up for Docker Hub
In order to use Docker Hub you must sign up for an account with Docker.