You can think of an image as a read-only template, which is the base foundation to run a container on. It's like a template that contains everything your application needs to operate. It can be Ubuntu Linux with a web server and your web application installed. Every image starts from a base image, for example, Ubuntu, a base Linux image. You can create images yourself - images are created using a series of commands (called instructions), described in the Dockerfile. It is an ordered collection of layers - root filesystem changes stacked on top of one another. These changes can be running a command, adding a file or directory, creating environmental variables, and so on. Docker uses a filesystem called AUFS, which stands for Augmented File System. Pretty much every line of a Docker file (with some exceptions, which we are going to explain later) will create a new image and when you stack or augment them all on top of each other, you'll get your final Docker image. This is essentially...