Know those records that you insert into a vinyl record player? Basically those, but pirated since a real one costs money when you purchase them at official music retailers. It involves the process of obtaining a legal copy then using wax molds (to recreate a record) and specialized tools (prevent quality loss) duplicating the record. (Also, “Bone Music” existed in the Soviet Union by printing music by using x-ray films).
I’d never heard of the discarded x-ray thing before reading your comment, and then it came up in a podcast I listen to about the world of marketing. This topic of this episode was Flexi Discs. Pretty neat topic I’d never heard of before.