Overpack means an enclosure used by a single consignor to contain one or more packages and to form one unit for the convenience of handling and stowage during transport. Examples of overpacks are a number of packages either: 1. placed or stacked on to a load board, such as a pallet, and secured by strapping, shrink-wrapping, stretch-wrapping, or other suitable means; or 2. placed in a protective outer packaging such as a box or crate.

Unit load means that a number of packages are either: 1. placed or stacked on and secured by strapping, shrink-wrapping, or other suitable means to a load board, such as a pallet; 2. placed in a protective outer enclosure, such as a pallet box; 3. permanently secured together in a sling.

IMDG Code definition

Marking and labeling of overpacks and unit loads

When dangerous goods packages are in overpacks or unit loads each individual packages must bear the marks and labels as required by part 5 of IMDG Code. If marks and labels representing dangerous goods within the overpack or unit load is not visible outside then replicate marks and labels outside the overpack with addition of word “OVERPACK” with letters at least 12 mm high.