Spells that are considered “dark” are of three types: Curses, Hexes, and Jinxes.
References from the canon
- The author said she used the word "jinx" if a spell effect was "irritating but amusing." Hexes are "slightly worse" (JKR).
- Curses are "the worst kind of dark magic" (JKR).
- Curses, jinxes and hexes are actually Dark Charms, according to Miranda Goshawk, Standard Book of Spells Grade 1 (Pm)