What does "Puppy Mill" mean?

What does “Puppy Mill” mean? That’s where the doctor thinks I came from. He says for sure I’m a Boxer… all Boxer is exactly what he said. I was 2 when I was thrown away. I lived in a shack where there were only a couple of other houses around, but those houses had windows and mine didn’t. This man kept trying to talk to me, but I was a little scared. I wanted to go to him, but I wasn’t sure. One day he took me into his home and made a phone call. About 30 minutes later a car pulled up and out came all of these people! There were 2 big people and 3 little people. I love little people!! I especially loved these little people. They were so nice and spoke to me in a way I could understand. In just a few minutes I was in the car… which scared me because my last car ride didn’t go so well. They took me to another home, where there was this little bitty dog. I won her over pretty quickly, but I’ve always been good at that. Now I have a fireplace, windows, doors, carpet…. and more importantly, I have my people. I get to protect them, play with them, and love them. Especially the little ones. They call me Rufus the Dufus. I’m not sure what a Dufus is, but they say it like they love me, and I love them too!