Define a docker image in 10 bullets points.

Docker image contains collection of file systems (root,user,application)
Docker image can contain one or many layers. rootfs layer is always present.
In case of file system conflict, the top layer takes precedence.
The layered file systems are identified using UUID which are created using SHA256 algorithm.
tagging is used to identify specific UUID with user friendly name
docker inspect command can show the UUID of various layers used in the image.
docker inspect command can be used to view docker image metadata
docker info command will show Docker Root Dir, where all the docker images are stored.
Docker merged directory is created when docker container process is started and it is removed when the container is stopped.
file changes made in docker container are persisted in “diff” directory which is used to re-create the merged directory when docker container is started next time.
docker rmi command can be used to remove docker image