It's usually just a general term for a long list of reasons why a pup doesn't make it. I had one out of 10 like this in the last litter. Was great for about 3 weeks then went down hill. Bottle fed, gave some supps, kept it hydrated. I concluded that the pup wasn't absorbing its food right and sadly after all that care I had to put it down. I probly hung onto it too long, I wasn't about to give up on it so quick though. They don't all make it. SO many things can go wrong with the creation of new life.