High Quality Content by WIKIPEDIA articles! Matrix numbers are alphanumeric codes (and on occasion, other symbols) stamped or hand written (or a combination of the two) into the run-out groove area of a gramophone record. This is the non-grooved area between the end of the final song on a record`s side and the label, also known as the run-off groove area, end-groove area, matrix area, or "dead wax".