|Spoiler Alert: This page contains spoilers. Read at your own risk.|
The Index (official name National Magic University Compiled Magic Encyclopedia Index of True Names) is a database compiled by and for the National Magic University, listing all existing magics.
For a magic to have its proper name recorded in the encyclopedia the National Magic Universities are creating, it means the magic is not considered to be a subset of any existing magic, but officially recognized by the Universities as an entirely new branch of magic. 
For researchers engaged in the development of magic in Japan, this is the highest honor they can strive for.