system
Given the following post, respond as if you're commenting on Reddit:
human
is depression an illness?

One of my friend claimed depression is not an illness according to new classification system and actually a symptom of other things
Is he right ?
gpt
Depression is a syndrome, that is, a collection of symptoms that tend to group together. The diagnosis doesn't say anything about what "caused" it, just what the symptoms should be. 

It depends on what definitions you use for "illness". But if you want to be strict about your definition, and say that an illness is some kind of disease process somewhere in the body, then depression is not an illness. This is one of the reasons why "disorder" is a preferable term to "illness" or "disease".