Zones in Permaculture

Hi! I’m very new to permaculture and I’m currently taking a certificate course for it. I’m curious about the types of zones used in permaculture designing. I initially thought that there were only 6 zones (Zone 0-5); however, I keep seeing in this subreddit mentions of zones up until Zone 7. I believe Zone 5 already refers to the wilderness, so what would Zone 7 be if that was the standard? Or am I mistakingly taking these zones in a different context hehe tyia!