Mac storage basics · iPhone and iPad backups and updates
What is an archived iPhone backup?
Short answer: A backup you've marked in Finder's Manage Backups so the next backup won't replace it — handy before updates. Each is a full copy, so delete old ones.
In Finder's Manage Backups list, you can right-click a backup and choose Archive. An archived backup is kept as it is and won't be replaced by the next backup — useful before a risky update.
Archived backups add up, because each is a full copy. Delete ones you no longer need from the same list.