Docker is an open platform for developing, shipping, and running applications. Docker containers separate your applications from your infrastructure, so your applications are portable and easy to run in different operating environments. A Docker image is a lightweight, standalone, executable package of software that includes everything needed to run an application: code, runtime, system tools, system libraries and settings.
Docker can build images automatically by reading the instructions from a
Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image. Using
docker build users can create an automated build that executes several command-line instructions in succession.
See Dockerfile reference for more details.
For more info on how to build and run Docker images see Docker Docs.