Preferment is a general term for something - usually fermenting - that is done before the final dough is mixed.
The first preferment was sourdough. Later preferments include autolyse, bigas, old dough, sponges, and poolish.
Baker folklore suggest that the preferments were developed after the introduiction of reliable bakers yeast in the mid to late 1800's. Bakers were happy to stop tending their starters and eagerly embraced the new techmology. However, two problems arose at once. Customers complained the bread no longer had as much taste, and the bakers hated having to pay the yeast companies every time the made bread. In the grand scheme of things, sourdough is free. All the starter that is made should leave the bakery as baked goods. Baker's yeast was seen as an added expense.
Luckily,both problems had the same solution. Instead of using lots of yeast in straight yeast doughs, by using very small amounts of yeast in a preferment and allowing it to ferment for an extended period of time, the yeast multiplies making a very active starter.
Preferments give many benefits to the baker. They build the taste in the bread, they make the dough easier to knead, they extend the life of the bread, and they reduce the amount of yeast needed to produce bread compared to a straight dough.
It is said that preferments came about shortly after the introduction of reliable bakers yeast, in the mid to late 1800's.