Matrix numbers..

..but not the ones falling down the screen in the movie you know.

These 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".

Matrix numbers are intended for the internal use of the record manufacturing plant, but they are also studied and documented by record collectors, as they can sometimes provide useful information about the edition of the record. This badly photographed series of numbers implies that the LP in the photo is called Solo Monk, original stereo version recorded 11/2/64 (Columbia CS 9149).

Now you know better ;)