Ambient music is minimal in the sense that it's just long-drawn out tones without any sudden change. It is great for background music as it can still convey a mood whilst requiring the least amount of attention from you.
Dark Ambient
Dark ambient music to me is linked to feelings of depression, determination, being at rock bottom, absolute focus and a sense that you can't run away from your problems anymore and that it's time to face them. As such, it's the music I listen to when I feel down, but need to be ready to work on something difficult.