A quick tour of Wikipedia articles on music that began at Schoenberg’s opera Moses und Aron:

Moses and Aron is based entirely on a single tone row, itself constructed from cells…

Okay, what’s a tone row?

In music, a tone row or note row (German: Reihe or Tonreihe), also series or set, is a non-repetitive ordering of a set of pitch-classes, typically of the twelve notes in musical set theory of the chromatic scale, though both larger and smaller sets are sometimes found.

Okay, what’s musical set theory?

Musical set theory provides concepts for categorizing musical objects and describing their relationships.

Right at the beginning of that article is a helpful illustration with this caption:

Example of Z-relation on two pitch sets analyzable as or derivable from Z17, with intervals between pitch classes labeled for ease of comparison between the two sets and their common interval vector, 212320

The reason we can’t have nice things in music is that only people who find this stuff absolutely fascinating are allowed to write serious music.