The term "mill puppy" is a slang expression used to describe dogs that are bred in large-scale commercial breeding facilities, often referred to as puppy mills. These facilities typically prioritize profit over animal welfare and keep their dogs in cramped, unsanitary conditions with little to no medical care or socialization. The term "puppies" is used loosely here because the animals are often sold at a young age without proper vaccinations or health screenings, which can lead to serious health issues later on. Overall, the phrase "mill puppy" refers to dogs that have been raised in inhumane conditions and may suffer from both physical and emotional problems as a result of their upbringing.