system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Difference between a 'disease', 'disorder', and 'syndrome'
gpt
* A *disorder* means that your body is not functioning normally
* A *disease* means that your body is not functioning normally, and science understands the specific process that led to that state. Everybody with the same disease undergoes the same basic process. There may be variations, but the underlying process is the same.
* A *syndrome* is a collection of symptoms. There is no guarantee that 2 people who have the same syndrome actually have the same underlying bodily process producing their symptoms. 
* Example: both syphilis and depression are disorders. Syphilis is a disease - science knows how it happens. Everybody with syphilis has been invaded by the syphilis organism. Depression is a syndrome - the process that causes depression is not clearly understood, and there is no guarantee that any 2 people who have "depression" actually have the same underlying physiology. 
* Example: a few hundred years ago, if you had a fever and were coughing up blood, people might say you have "hot blood coughing up syndrome." Today, we know that some people with this syndrome have lung cancer (a disease) and some of them have tuberculosis (a different disease) and some of them have other things.