MINIMAL—a simple cover that is usually object based.
SIMPLE—just a simple cover with some text on it. some call it text slap.
VECTOR—covers without real people in it. sometimes people trace over pictures of people and make their own vectors. I usually Google them and get free people vector PNGs. or simply cartoonish covers. I like to use silhouettes.
MANIPULATED—these are very complex covers with multiple layers and I suck at manips. getting textures from wattpad and websites help A LOT.
that may be a semi manip actually. I suck at manips. sorry I don't have a good example.