a laborer who builds up a stack or pile
"The new stacker at the warehouse moved so quickly that he cleared an entire pallet of crates before lunch."
Any person or thing that stacks.
"The warehouse manager hired a new stacker to organize the pallets before shipping them out."
A worker who stacks the shelves in a supermarket.
"After his shift at the grocery store, he wiped sweat from his brow and thanked the manager for letting him finish stocking the cereal aisle as the last stacker before closing time."