Reality bubble

A reality bubble was a kind of technology.

Gallifrey continued to exist at the exact end of the universe with part of the Cloisters still being intact and used by Me to watch the end of everything, preserved by a reality bubble. After Me discussed the Hybrid with the Twelfth Doctor, the two left in the TARDIS he had acquired, after which the reality bubble gave out and the universe finally ended. (TV: Hell Bent)