A kill or half-kill is when the casino temporarily bumps up the limits for the next round of play. For example, in a $4-$8 hold 'em game with a full kill, if someone wins two pots in a row, that player is required to post an $8 blind and the limits for that round or rounds (until someone else wins a pot) double to $8-$16. In a half-kill game, the limits are raised by 50%, so it would go from being $4-$8 to $6-$12.
There are different rules, but most cardrooms follow these guidelines for kill games: 1) In hold 'em, a player who wins two pots in a row initiates a kill for the subsequent round or rounds; 2) in Omaha, a person who "scoops" the pot by winning both the low end and the high end of the pot initiates a kill. Kill games are not frequently found in other poker game types.
A kill gives players the opportunity to try a higher-level game while still being able to stay within their bankroll. Kill games often spur more action, because a kill generally leads to three blind bets instead of the normal two. (If the big blind or small blind is the "killer," then there will still be only two blinds). This means there's more money in the pot prior to the flop, giving people incentive to try to steal or to play marginal hands for a big return.
