A plant was usually a set of buildings, purpose-built, and originally for power generation, chemicals manufacturing, refining and smelting metals, cement-making, meat packing, food processing, beverage manufacturing, etc
A factory, manufacturing plant or production plant is an industrial site, usually consisting of buildings and machinery, or more commonly a complex having several buildings, where workers manufacture goods or operate machines processing one product into another. The word factory generally refers to a production site where a specific item is produced, whereas a plant refers to a site where a specific process takes place.