What does 'resi' mean in M+?

Ive noticed some keys writing resi in the title, what does that mean

Blizzard added a new achievement line with today’s build: Resilient Keystone! As previewed in their earlier blog about Mythic+ changes in Season 2, once you complete all dungeons at +12 or higher, your keystone can no longer drop below that level. To better track this, there are separate achievements, one for each keystone level starting at +12.

So resilient means the key can’t depelete.

So mentioning that in the title is meant as an encouragement to apply because you can’t deplete the key holders key?

Yes, it attracts people to join because they know they can reset the dungeon and try again if they fail.

Ha ha, of course, how could I think it should encourage players who are uncertain whether they are really up to the content or not.
I still don’t have the proper M+ mindset yet.