What is the difference between depression and just being sad?

Typical person test: Sadness is a normal human emotion expressed under appropriate psychosocial circumstances. Depression is a disorder that causes one to derive no pleasure out of usual activities, to be unmotivated, to not care, to be unproductive. To see gloom where there is none. To be flat, unable to have appropriate emotion. If youre concerned about being depressed, see your doctor right away. It's treatable.

Depression: Sadness is feeling that lasts briefly, while depression lasts significantly longer and is among a constellation of other symptoms.

Dep. vs. sadness: Neurovegetative signs/symptoms as well as longer duration, differentiated major dep. From sadness alone.