I just stumbled across this question and saw that nobody has ever answered you.
Hopefully, you have gotten your answers by now, but in case you haven't, I will try my best to answer it.
Major Depression is most often called Clinical Depression. or Major Depressive Disorder. There is a specific set of symptoms that a doctor would look for in a diagnosis. It also must have been going on for at least three weeks. People that suffer from clinical depression, tend to struggle with it for a long period of time.
As for Minor depression, I think there is still some dialogue going on over whether it differs from major depressive disorder in any clinically relevant ways. For the most part, it appears the symptoms are the same as clinical depression but less severe.
I hope this helps!