system
Given the following post, respond as if you're commenting on Reddit:
human
A fever “breaking” is a term used commonly to describe a cold or illness going into a less severe phase, and is even used in medical papers, what if any is the scientific measurement to quantify it “breaking”?
gpt
In medicine having a fever or being “febrile” is generally considered to be a temperature greater than 100.4F. Sepsis criteria includes fever of more than 100.4°F (38°C) or less than 96.8°F (36°C) as hypothermia can be a sign of infection as well. 
A fever “breaking” is a layman’s term and is also outdated as it really has no meaning in modern medicine. It’s based on the notion that some illnesses often accompany a fever and after it (a self limiting virus) runs its course the fever resolves as the body recovers. 
But you should know that the fever is NOT the illness. Fever is just a response by the body. Just because a fever ends does not mean the illness is ended. Different illnesses have different patterns. Some may have a constant fever, some intermittent, some have recurring patterns of days or months. And treating a fever is not usually necessary aside for comfort reasons unless it gets severely high around 105-106 where febrile seizures are a concern, especially in babies/children.