division of labor

Narrow specialization of tasks within a production process so that each worker can become a specialist in doing one thing, 
especially on an assembly line. 

In traditional industries (see sunset industries), division of labor is a major motive force for economic-growth. 

However, in the era of mass customization (which requires multiple skills and very short machine change-over time), 
division of labor has become much more flexible. 

Also called specialization of labor.

from www.businessdictionary.com