In Fedora Silverblue, the term "rebase" is used instead of "upgrade" to emphasize the unique way the system handles major version changes. Unlike traditional upgrades, rebasing in Fedora Silverblue involves switching to a new, immutable base image of the operating system. This process ensures that the system remains stable and can be easily rolled back if something goes wrong. The term "rebase" is more accurate because it reflects the underlying technology (rpm-ostree) that manages these immutable images, allowing for atomic updates and rollbacksfedoramagazine.org+1.