This image from the Docker website (http://www.docker.com/) gives information on how and why the Docker team feels their technology fits into the future of application development:

The preceding image, concisely describing the generational shift in application architecture we are now experiencing, can just as easily be used to describe the how and why of Node's design.

Docker, according to the website, …is an open source engine that automates the deployment of any application as a lightweight, portable, self-sufficient container that will run virtually anywhere. Once you have created a Docker image of your application, a running instance of that image can be spun in milliseconds. Yes, that's right: a few milliseconds. Docker lets you create even hundreds of deployments of your application in a few seconds.

The Docker ecosystem has three main components. Here's some information about the components from the documentation: