What is the difference between "sadness" and "depression"?

What is the difference between "sadness" and "depression"?

The terms depression and sadness can be confusing, and some people use them interchangably, however there are important distinctions. Sadness is really a universal phenomenon; everyone can relate to what being sad is like. However, depression really refers to something more profound. In Psychiatry, when we talk about a person being depressed, we are not only talking about a mood state, but we're also talking about physical symptoms, such as problems with sleep, appetite, the ability to enjoy things. We also see other characteristic things such as worthlessness and hopelessness, which we don't see typically when a person is just experiencing a sadness.