A puppy mill is often characterized by inhumane conditions, particularly for the "breeding stock" animals who are caged and continually bred for years, without human companionship, and then typically killed after they can no longer produce puppies.  

Have a look at this website for more information about puppy mills.  You can chat with many different people about many different dog related issues, not just puppy mills.  The website is:
 www.nopuppymills.com