Sphere
From UnderlightWiki
A unit measuring the experience level of a dreamer, in addition to orbits. One sphere is equivalent to ten orbits.
Spheres form the basis for many restrictions in the city, most notably portals that are restricted only to higher sphere levels.
Once a dreamer reaches each ninth orbit, they must find a teacher that has the ability to train sphere levels, and is of a higher sphere level than the student. The student will be required to complete an arduous task before the teacher advances them to the tenth orbit.
The sphere equivalent in arts are referred to as plateaus. The same process applies.