Mass production is the production of large amounts of standardised products on production lines. It was popularised by Henry Ford in the early 20th Century, notably in his Ford Model T.
Pre Industrial Revolution
While Ford was first to introduce mass production to the industrial age, the idea was first developed in Venice several hundred years ealier, where ships were mass-produced using pre-manufactured parts, and assembly lines.
The Venice Arsenal apparently produced nearly one ship every day, in what was effectively the world's first factory that, at its height, employed 16,000 people.