What is a straddle bet?

In limit Hold'em and other flop games players are frequently allowed to make a bet called a straddle bet, sometimes known as a live blind, live raise, or live-<amount> where <amount> is the amount of the bet. The player who follows the big blind and would normally be under the gun can raise before cards before cards are dealt. Players that act after him must call the raise, fold, or raise the bet themselves. The straddler's raise is live - if no-one else raises, s/he has the option to reraise after the blinds have acted. If straddle bets are allowed, the player behind the straddler can also post a straddle by raising again, and so on until the maximum number of bets is reached.

For example: In a 6-12 game, the blinds are 3 and 6, the player after the small blind makes it live-12 by raising before the cards are dealt, and the player after him can make it live-18.