Docker Engine is a free containerization platform for developing and deploying applications. It is a client-server program running on top of dockerd, a long-running daemon process. It includes APIs that define interfaces for software to communicate with and instruct the Docker daemon as well as the CLI client docker.
With scripting or CLI commands, the CLI client uses Docker APIs to monitor or communicate with the Docker daemon. Many other Docker applications use the underlying API and CLI. Also, it is the daemon that creates and controls Docker objects such as images, volumes, and so on.
