How exactly is dysthymia different from major depression?

Dysthymia: Dysthymia and major depression are related, but dysthymia lasts 2 years or more. Also the new dsm 5 calls dysthymia "persistent depressive disorder.".

Type of depression: Dysthymia, is a chronic type of depression that doesn't waver all that much in terms of intensity, as opposed to major depression which wavers widely in intensity. Metaphorically speaking, those with dysthymia experience it as having to wear a coat made of lead, 24-7, with little variation. Those with major depression experience the depressive lows almost like waves.