What's the difference between minor depression or major depression?

Major depression: Involves physical signs of a physical illness called major depression. So changes in sleep, appetite and/or energy are the things we look for.

A milder form of MDD: Minor depression is a mood disorder that does not meet full criteria for major depressive disorder but in which at least 2 depressive symptoms are present for 2 weeks or more. It is usually quite responsive to psychotherapy interventions. In the diagnostic & statistical manual of mental disorders iv, minor depressive disorder was cited as an example of depressive disorder not otherwise specific.

Yes: The simple difference is the number of symptoms that you have. The practical difference is that there are far more studies out there about treating major depressive disorder so we better know how to advise people.

Depression: Minor depression is an old term for less severe depression, now called dysthymic disorder.