What does "image immutability" mean?

Image immutability means that an image cannot be changed after it has been created. It is "frozen" in the form it was built in. If something needs to change (adding a package, updating a config, etc.), Docker does not edit the old image, but creates a new one based on it.

#Why this matters (junior level)

• Predictability - the same image always starts the same way.
• Repeatability - it's easy to reproduce the environment on any machine.
• Security and version control - you can keep v1, v2, v3 and know what's inside, without unexpected changes.

In short: Immutability = the image cannot be changed, only a new one can be built, so it always stays stable and predictable.