A pallet jack, a.k.a. a skid jack or stacker, is a simple type of forklift designed for use in warehouses. Unlike a fancy forklift which has a cab and various power assistance, the typical pallet jack is a simple manual device for picking up a load atop a standard skid and moving it around the warehouse, or in the case of the stacker, taking it to/from warehouse shelving.
The pallet jack has a pair of flat metal prong arms that rest parallel to the floor. These arms, or forks, are three to four feet long, and are usually painted a bright yellow or orange for safety. At least they start out that way, though with usage they tend to shed a lot of that paint and take on a patina of grunge. At the front of the prongs are small wheels. At the back, the prongs connect to a wheeled central steerage and balance point at which the jack and its load can be pushed, pulled, or turned as required.
At rest the prongs are a couple of inches above the floor, just the right level to slide inside a standard pallet. On the basic model, a hydraulic pump in the handle can be worked to raise the forks in increments, while the front wheels drop in sync to keep the load level. A lever in the handle is used to release the hydraulics and let the prongs descend back to the floor once the load is delivered. Fancy jacks may have a power assist to raise/lower the prongs.
Most pallet jacks lift only enough to provide a small amount of floor clearance to their loads, sufficient to get the pallet off the ground and transport it around the nicely level floor of the warehouse. The stacker has a separate lower frame where the wheels are, and can lift much higher. It is be stabilized to allow it to raise pallets onto, or retrieve them from, shelving.
Powered pallet jacks are usually electric. These are used to move larger or heavier loads than can be moved with the manual pallet jack. They are certainly never used to hold warehouse races. Nope.