Concept: Unit Load

Pallets and containers are two most commonly used material handling equipment, used to provide the right material at the right place and within the right cost. Several firms today have adopted just in time programs as a result of which the combination of containers for parts distributed on pallets has gained more popularity. A basic principle of material handling is the concept of unit loads. A unit load is a number of items arranged as one unit, to be moved or handled at one time. In effect, the unit load implies the container and the support platform or pallet. The main advantage of using unit loads is the ability to handle more items at one time. This reduces the number of trips, handling costs, loading and unloading times as well as product damage. The most flexible and multi-faceted material handling systems are the Automated Guided Vehicles (AGVs) and have a variety of functions such as guidance and routing systems to traffic management and load transfers.

Reference:
http://www.materialhandlingblog.com/2006/01/the_concept_of_.html