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. A Container image is a static template version of a Docker Container, it is stored in the Docker registry. 

Container images become containers at runtime and in the case of Docker Containers - images become containers when they run on Docker Engine.

When we execute the $ docker run command the container image is fetched from the registry and loaded in the Docker Daemon server to make it a live executing container.