Container image
Also called: Docker image, OCI image
A packaged, read-only snapshot of an application with everything it needs to run, built in layers and started as a container.
Definition
An image is built from a Dockerfile (or by Buildpacks) as a stack of layers, each the result of one build step. Layers are cached and shared, so putting rarely changing parts (the base image, dependencies) first and the application code last means a release only ships a few megabytes. Images are tagged and pushed to a registry, and should never contain secrets.
In practice
registry.example.com/checkout:3f9a2c1 is the checkout service built from commit 3f9a2c1.