Rolling Update vs Revisions

Hello,

This question is about Lesson 9, Deployments (II).

I am confused about the term revision.

The lesson states that a revision is triggered as a result of a planned action, such as an update in the container image, port, volumes, mounts... Whereas a change in the deployment template (ie update in the container image) would trigger a Rolling update.

I am confused when the lesson states that after the Rolling update has been implemented, K8s records the prior state changes of the Deployment as a Revision.

I would appreciate if someone could kindly shed some light on this.

Thank you.