Definition of feeler bet
A feeler bet is also called a "tip bet" by some players. In poker, you can bluff a bet because your hand is weak, but you think your opponent will fold. You can bet because you have the best hand often and your opponent could call with worse, but you can also bet to "see where you stand. We bet an average hand to see what our opponent does. If he raises, we fold, if he folds, we win the pot. Betting without knowing whether you are in value with a good hand or bluffing is called a "feeler bet".
The feeler bet, in moderation
The feeler bet is definitely 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 the feeler bet will only make you lose money. Also, betting without knowing whether you are bluffing or making a value bet will make the poker game bigger for nothing. And if your opponent raises you with a draw, you'll have to fold an average hand that you could have taken to the showdown.