Definition of feeler bet
A feeler bet is also called an "info bet" by some players. In poker, you can bluff a bet because your hand is weak, but you think you're going to fold your opponent. You can bet because you have the best hand often and your opponent might call with worse, but you can also bet to "sit". You bet an average hand to see what your opponent is doing. If he raises, we fold, if he folds, we win the pot. Betting without really knowing if you're in value with a good hand or bluffing is called a "feeler bet".
The feeler bet, in moderation
The feeler bet or the bet for info is certainly a game to be played in moderation. Most of the time, if you are against a good player, he will put you in a difficult situation and feeler bet will only make you lose money. Furthermore, betting without knowing whether you are bluffing or value, will make the size of the poker game grow for nothing. And if your opponent raises you with a draw, you'll have to fold an average hand that you could have brought to slaughter.