Reverse Komi
Komi given to Black, the starting player or the player receiving a handicap.
Robert Pauli: Instead of speaking of reverse komi one can also allow the value of (normal) komi to drop below zero, e.g.
- 6 points reverse komi = -6 points (negative) komi
To give Black 6 points is, of course, the same as "giving" White -6 points (I know I'm being silly here).
Now that we allow the full range, it would be more logical to turn the sign of komi (at least in my opinion). To increase a handicap would then either increase the number of handicap stones or increase the komi (or increase both).
But, of course, we're used to even games? played with 5.5 komi or the Nihon Ki-in increased komi to 6.5, so it seems easier to keep it this way.
For an example of negative komi at pro level see Amateur Honinbo vs Pro Honinbo 2002.
Andre Engels: Negative komi is mostly used at smaller board sizes, because a more fine-grained difference is needed - between two players n stones on 9x9 might be clearly better than 50% winning for White, but n+1 clearly offer better chances for Black. Depending on the more exact differences, they could then play n+1 stones with komi for White or n stones with reverse komi.
Robert Pauli: Actually, negative komi should be used on the 19x19 as well, Andre. In fact, every handicap game should have negative komi - provided the ranks are one stone apart and handicap stones lack synergy (behave linear):
gap = 0 -> "handicap" 0.5 = place 0 and receive 6 (i.e. give -6) gap = 1 -> handicap 1.5 = place 1 and receive 6 gap = 2 -> handicap 2.5 = place 2 and receive 6 ...