Is it sadness or depression? What's the difference?

Depression is different from being sad.  Being sad about sad things in our lives is normal and expected.  Sadness is a temporary feeling that goes away, usually on its own. If you didn’t get into the college you wanted, it's ok to be sad about it.  If you’re fighting with a friend, if there’s trouble at home, sadness is not a bad feeling to have. 

Depression is a mood disorder.  It is a persistent unrelenting sadness that affects your quality of life and interferes with your ability to do your day to day activities

Sadness is a normal reaction to loss, disappointment or any difficult situations.  If you are having a fight with your spouse, boyfriend, parent etc., tears and sadness are normal.  This is human. Sadness passes with time.  In general, if persistent sadness is around for more than 2 weeks, you should talk to someone. Usually a person experiencing sadness can find relief in crying, venting or talking out frustrations.  Depressed people can't always find that relief..  Sadness is a component of depression, but it it alone is not depression

Depression is a feeling that nothing matters that is so strong it interferes with one’s ability to function in the world. School? Work? Social life? Depression can make getting out of bed every morning like climbing Mt. Everest. 

People who have Depression are often filled with negative repetitive thoughts and they just can’t shake it.  It is a very complicated disease in that it affects neurotransmitters in the brain. It's not hypothetical, there are often chemical changes in the brain.  It's not just the chemical imbalance, it's the psychological and emotional aspects to it.