A single SaaS instance can move between these three levels. Typically, from Preview, to Release, to Stable, to Long Term Stable, and then can move back to Stable if an Stable update is applied.
Preview - Updated regularly. New features added often.
Release - Updated regularly, usually on Sundays. Feature locked.
Stable - No new updates applied for 30-days, and non-expected for the next 60-days.
Stable Patched - Important software maintenance or security update applied - Returns to stable after 7-days of no software patch issues. This is a new patch for an immediate concern.
Long Term Stable (LTS) - No new updates applied or required for the past 90-days
Stable (again) - New stable software update applied. Return to LTS level after 90-days without an update.