Docker is a group of PaaS (Platform as a Service) products that are used to containerize the application or software or package them into containers for deployment within a bundle which consists of libraries, and dependencies that are required for the application’s proper working. A Registry stores information that is specific to the task it was created for. A Docker Registry stores information such as Docker Images, for versioning, storing, and distribution of those images. DockerHub is the official hosted registry while installing Docker Engine. You could opt for other registries if you like depending on your requirements.
If you wish to learn more about Docker, check out the Docker tutorial and if you wish to get skilled and certified in Docker, then check out the Docker training course from Intellipaat. Also, check out the YouTube video on Docker Interview Questions, if you wish to prep up for any Docker interview.