What do the members here think or believe constitutes a puppy mill?

Is it the number of puppies? Number of dogs used for breeding purposes? Conditions that the dogs are kept in? I just visited a site that sells its dogs all over the US.
The dogs that are not currently breeding are kept in a steel building on a cold, cold concrete floor, in kennels. There were about 35+ adult dogs. Of the nursing moms and puppies, I found them just laying on a container under incandescent lighting (for warmth, I imagine). The puppies that were walking around just didn't seem right, at least not what I had experienced with my own little girl's pups.
My own little girl Abbie-Gale had five baby girls in October and the last one has now left to her forever home. This was our first litter and I really had a great time watching them grow. They were raised in our home and pottytrained by the time they left.
I am disappointed because I was looking for a boyfriend for my Abbie.