The distinctive characteristic of factory farms is the intense concentration. Note how in America it is much more concentrated to certain areas than in China or Europe. This is because we have more factory farms than those areas.

Factory farming is the practice of raising livestock in confinement at high stocking density, where a farm operates as a factory

The main product of this industry is meat (mainly chicken and pigs), milk and eggs for human consumption.

Factory farms are usually associated with pig and chicken meat production

Description
Confinement at high stocking density is one part of a systematic effort to produce the highest output at the lowest cost by relying on economies of scale, modern machinery, biotechnology, and global trade. Confinement at high stocking density requires antibiotics and pesticides to mitigate the spread of disease and pestilence exacerbated by these crowded living conditions. In addition, antibiotics are used to stimulate livestock growth by killing intestinal bacteria. There are differences in the way factory farming techniques are practiced around the world. There is a continuing debate over the benefits and risks of factory farming. The issues include the efficiency of food production; animal welfare; whether it is essential for feeding the growing global human population; the environmental impact and the health risks.


Distinctive characteristics
Factory farms hold large numbers of animals, typically cows, pigs, turkeys, or chickens, often indoors, typically at high densities. The aim of the operation is to produce as much meat, eggs, or milk at the lowest possible cost. Food is supplied in place, and a wide variety of artificial methods are employed to maintain animal health and improve production, such as the use of antimicrobial agents, vitamin supplements, and growth hormones. Physical restraints are used to control movement or actions regarded as undesirable. Breeding programs are used to produce animals more suited to the confined conditions and able to provide a consistent food product.


For more details including details on environmental impact, health concerns and ethical issues, please see:
http://en.wikipedia.org/wiki/Factory_farming (external link)