When most people think of depression as a mental disorder, they are thinking of depressive disorders, which include major depressive disorder, dysthymic disorder and depressive disorder not otherwise specified. There is also a major depressive episode that involves depressive symptoms. The word “depression” can be used in everyday language to imply feeling sad, unhappy or “down” for a short period of time, but being depressed in this sense doesn’t necessarily mean you have a mental disorder.
The National Institute of Mental Health’s website states that there are three main types of depression: major depression, dysthymia and bipolar disorder. In the DSM, these are called major depressive disorder and dysthymic disorder, and bipolar disorder is considered a mood disorder. The website adds that general symptoms of depression include feeling sad, anxious or lacking feeling, having problems concentrating and remembering, feeling restless and irritable, having headaches and digestive issues.
https://www.empowher.com/mental-health/content/what-depression