Definition of cbet
A cbet is a term introduced by Dan Harrington in his famous poker tournament trilogy. Basically, a cbet is a bet you make when you are the preflop aggressor. The cbet is a bet that the player who raised preflop can make (or the player who made the last aggressive preflop action). In this situation, the player is said to have the lead. You must have the lead to be able to cbet. If the pot is open-ended, the bet is called a bet and not a cbet.
Additional details on cbet
Generally, when a player has opened preflop and his opponent has called the bet, he will do what is called a cbet on the flop. If the bet is called and the player bets the turn, then the player is said to cbet the turn. The majority of players cbet too often. The mentality behind the cbet is "I raised preflop, I showed strength, you just called, so I have a better hand than you and I'm going to bet it (cbet) on the flop. You can cbet the flop, turn and river.