A definition for the lay person
A pallet jack is a device designed to easily move heavy objects from one place to another, with two adjustable-width forks (controlled by a hydraulic arm) that slide underneath a pallet and lift it into the air. Pallet jacks, used in manufacturing plants, warehouses, and storage facilities, are often simple to operate and can support huge amounts of weight.
There are two kinds of pallet jacks, manual and powered. A manual pallet jack looks like a dolly with two forks attached to the front. The pallet jack is controlled by the operator, who stands behind it and manipulates direction with the use of some type of steering implement. Once the two forks are underneath the pallet, the operator initiates lifting with the use of a lever. The object can then be walked to its new location. Manual pallet jacks are best for places in which pallets are stored mainly on the ground.
An electric pallet jack is preferable for a situation in which pallets are in high pallet racks or stacked in twos or threes. With a small platform for the operator, an electric pallet jack uses a motor to power its hydraulic arm, offering added strength and greater control and stabilization. The operator uses a throttle to move the jack back and forth and to control the pallet's angle on the forks.
Some powered pallet jacks, called pallet trucks, are similar to forklifts in that they offer a seating area for the operator. Pallet trucks also offer the same maneuverability as a forklift but are often built only for indoor use.