Matrix number

Stamped matrix number on a vinyl album with the film score for Diamonds are forever

A matrix number is an alphanumeric code (and on occasion, other symbols) stamped or handwritten (or a combination of the two) into the run-out groove area of a phonograph record. This is the non-grooved area between the end of the final band on a record's side and the label, also known as the run-off groove area, end-groove area, matrix area, or "dead wax".