A transmaterial energy plane is a type of spatial domain.
"Galactic Cluster 3" was the Borg designation for such a realm, which intersected 22 billion omnicordial lifeforms. The Borg encountered Species 259 in this cluster, from which they assimilated autonomous regeneration sequencers. This technology was later installed by the Borg on the USS Voyager in 2374. (VOY: "The Gift")