Key Docker Concepts

Dockerfile
Docker can build images automatically by reading the instructions from a Dockerfile. A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image.
Docker Image
An image is a filesystem and parameters to use at run time. It does not have a state and it never changes.
Container
A container is a running instance of an image.
Data Volumes
A data volume is a specially-designated directory within one or more containers that bypasses the Union File System.
Data volumes are designed to persist data, independent of the container’s life cycle. Docker therefore never automatically deletes volumes when you remove a container, nor will it “garbage collect” volumes that are no longer referenced by a container.