These are my own delineations, and are by no means official definitions, but here's my best shot:

Romance is when the focus is on the relationship between a couple, like the movie Titanic, whereas fluff is something that gives the reader a warm and fuzzy feeling while reading. They can overlap (like with romantic comedy) but not always.

Angst is more emotion-driven, especially if that emotion is anxiety or dread, whereas drama simply describes a feeling of excitement.

"Dark" means a fic that involves tragic themes, whereas "death" requires a character to actually die.

Does that help?