[DeadRed]

I have had the sense that a value bet is the largest bet that your opponent will call after the river when they are beaten. Assuming you have read the hand perfectly due to the board, bets, position, etc. and know that you are winner, you want to bet an amount that your opponent will call. You want to maximize this amount, but go too high and you get nothing (other than the pot, which is yours anyway). This definition, of course, does not apply to limit games. Maybe this is one application of a "value bet", but it is where I have heard it applied.