Docker image
A practical DevOps definition, with an example you can use.
A read-only template of filesystem layers and configuration used to create containers.
An example you can picture
A Dockerfile installs dependencies and copies application code. Building it produces an image; running that image creates a container. The registry stores images for other systems to pull.
The distinction that matters
A mutable tag such as latest can point to different content over time. An image digest identifies specific content more precisely.
Put it into practice
Compare the image reference in a Dockerfile, a build output, and a running container. Identify the tag and digest where available. Explain how you would reproduce the same release later.
Connect the ideas: container and artifact. For the bigger picture, read the related learning guide.
Reference
Read the primary documentation for the underlying concept and further detail.