What is Docker Engine?

Docker Engine is the core mechanism of Docker that runs and manages containers. It handles the creation, startup, stopping, isolation, network settings, and storage of containers and their images.

It consists of three key parts:

1. dockerd (the daemon) - a background process that does the main work: manages images, containers, networks, and volumes.
2. Docker CLI - a console interface (the docker command) used by a person. It sends requests to the daemon.
3. REST API - an interface through which the CLI and other programs communicate with the daemon.

How it works in one sentence: CLI → (request) → Docker Engine → (result) → running container.

In other words, Docker Engine is the "heart" of Docker that carries out all container operations.