Container image

A Container Image is an immutable, content-addressable package: it bundles the application code, dependencies, and execution configuration into a single, portable artifact.

The Container Image is the foundational technology for modern application delivery, standardized by the Open Container Initiative (OCI) Image Format Specification. It operates as a stack of read-only filesystem layers (diffs) which, when combined, form the container's root filesystem. This layered structure ensures efficient storage and distribution, as only changes between versions are transmitted. A separate configuration object dictates the container's runtime parameters: this includes the entrypoint command, default arguments (CMD), and environment variables. Tools like Docker and Podman use this OCI standard to guarantee consistent execution across any compliant host or cloud environment.

https://opencontainers.org/documents/image-spec/