The process by which changes to content are saved as a new copy of the content, instead over over-writing the existing state of the content.
A single instance of a content object at a moment in time is referred to as a version. The collected versions of a single content object are the version history or version stack.
By versioning content, the CMS retains a history of all the changes to a piece of content over time allowing editors to rollback to prior versions if necessary or audit changes to content for security or regulatory purposes.
Versioning and version control are often confused and used interchangeably.