quantity mail that is rated by bulk (aggregate weight), rather than by the piece, although minimum per-piece rates apply.

a way of sending multiple copies of a publication, direct mail letter, or other items through the postal system under a permit or pre-canceled stamps; certain requirements and restrictions apply as to number of pieces, weight, and preparation for mailing.

sending a large number of identical pieces of Third Class Mail at a further reduced rate; requires special sorting and labeling.