The meaning of this Latin prefix, Terra, pertaining to the Star Ways is best explained in the following link:
Namely, Terra means a rough upland or mountainous region of a solar system body often having a high albedo relative to other surface features. Terra also means earth, land. The concept ‘albedo’ has particular significance for the Terra of the Star Ways. The term ‘albedo’ refers to the fraction of incident electromagnetic radiation reflected by a surface, especially of a celestial body.
For further information on albedo refer to:
The sphere of Terra is governed by the human race, which has some notion of atomic energy, but none of biophotonic energy. In the sphere of Terra, the biophotonic spiral of a spirem is hampered by ‘atomic adaptations’ made by its humans, and hence spirems prefer to dwell in the sphere of Quanta.
In short, the Terra of the Star Ways is the sphere which represents the ‘real time’ world of the characters. It spirals in co-existence with the other two spheres of the Star Ways.