What is a Half-K event? (As mentioned in rating documents.)
Steven Craig Miller
Previously events were allowed to be rated as half-k, that is players’ ratings would change at half the rate that one might expect. I don’t believe that they exist any longer.
Alex Relyea
From the entry/edit tournaments screen in the Tournament Directors Area:
“(The K factor applies to Regular Ratings only.)
Note: 1/2 K will no longer be available for events ending after Feb 28, 2006.”
If I understand correctly, in the days before Quick ratings, if an organizer shortened the time control significantly they might offer it as a Half-K, so that players wouldn’t be risking as much in their rating on those dadgummed too-fast-play events like G/30. (Before my TDing and tournament playing time, though, so I am very willing to be corrected… 
)
Kasparov offering Rook odds.
That’s a Special-K event.
Thanks!
Steven Craig Miller