A container is an application sandbox. Each container is based on an image that holds necessary configuration data. When you launch a container from an image, a writable layer is added on top of this image. Every time you commit a container, a new image layer is added to store your changes.

An image is a read-only layer that is never modified. All changes are made in the top-most writable layer, and the changes can be saved only by creating a new image. Each image depends on one or more parent images.

A platform image is an image that has no parent. Platform images define the runtime environment, packages, and utilities necessary for a containerized application to run. The platform image is read-only, so any changes are reflected in the copied images stacked on top of it.