this might be a dumb answer...but this is what
i consider a back yard breeder...we have some right down the street from us
they have SEVERAL dog pens in their back yard. they are not cages, but they are pens. rows of them. maybe 30 pens all together. maybe more..maybe less...but that is my guess. they have several different breeds. the dogs all have a dog house in the pen as well as food and water.
i honestly dont' know the "technical" difference between a byb and a puppy mill...but i consider the people down the street from me to be byb's
now...a reputable breeder...that's a whole different category in my book. they are the ones who have personal contact and relationship with each dog...they care for the dog and not the money. they have one breed of dog..and give the dogs proper care, attention, and love...and i could go on and on.
now...these are just my opinions...i'm no expert