Definition of value cut
When a player makes a value cut, it means that he thinks he is making a value bet, but in fact he is making a bet against a hand that is better than his own. Instead of making more money from his bet, he loses a bigger pot. This can be the case when a value player bets too thin. For example, a player who bets flop, turn and river with KJ in hand on K-2-2-5-Q and is called on the river by AK is a value cut player. In this situation, except for perhaps a hand like KT, there are few hands that will call that will not dominate KJ.
Value bet thin against nits
If you are against a "nit" (a very tight player) and you bet on the flop, turn and river, you will need to have a very good hand. Betting three times with an average hand and hoping to get called by a lesser hand is a pipe dream. To avoid a value cut, when betting three streets, make sure you have a very strong hand or are playing against a player who is a calling station type and calls too much.