The term docker is often thrown around.   It turns out to be fairly complex as a it crosses

across the developer, qa, release, and system admin roles.

Its supposed to make all these easier and more consistent.

So

1. Docker is a unix/linux/macos command line utility

    It provides utilies to push, pull images, start up the image, stop the image , remove the image. 

2. Dockerfile is a file that specifies how to create an image for distribution.

    This is used at the point of release. 

3. docker-compose is a command line utility that processes the file docker-compose.y[a]ml

    docker-compose.yml defines a development environment that  developer can use

    to edit/add/manage code.