"A large-scale industrial site where many animals (generally chickens, turkeys, cattle, or pigs) are confined and treated with hormones and antibiotics to maximize growth and prevent disease. The animals produce much more waste than the surrounding land can handle. These operations are associated with various environmental hazards as well as cruelty to animals."
The cheap chicken that has become so ubiquitous to the dinner table in various bits, pieces and stages of pre-cookery is generally raised with no more floor space than the size of a sheet of paper. It is crammed in with other birds so that none of them have room to move. Their beaks are usually cut off to prevent them from hurting each other (or themselves) and they are kept in the dark. Add to that the constant dosages of vaccines, antibiotics and hormones that make their way into our bodies and water systems. Read more about it here - What is a Factory Farm?
Another thing to keep in mind is that most "store-bought" critters are fed some horrible things - poop, body parts, garbage, plastic, blood, road kill, even euthanized pets! All completely legal. Cows are fed chicken bedding, and "...pig carcasses can be rendered and fed back to pigs, chicken carcasses can be rendered and fed back to chickens, and turkey carcasses can be rendered and fed back to turkeys. Even cattle can still be fed cow blood and some other cow parts."
I'll spare everyone the actual pictures of factory farms and descriptions of what all the manure and dead animals they generate does to our environment. See for yourself here Animal photo gallery and here Animal waste "treatment".