Definition of OTB
OTB stands for "On The Button". Being OTB gives us a huge advantage over our opponents since we will have maximum information. Preflop, if no one has made a raise, the OTB player is in a good position to steal the blinds. If we have an interesting, but not exceptional hand, we can get a good look at the preflop action. For example, a player with 77 in UTG position will raise to 3 big blinds. If the two players after him 3-bet and 4-bet, he will be forced to fold and will lose 3 big blinds. If this player had been on the button, he would have simply folded his hand.
OTP, a preflop and postflop advantage
Postflop (after the flop), the OTB player will also be the last to speak on all streets. So he'll be in a great position to bluff if all players have checked, he'll be able to make big folds if there's too much action before him, he'll be able to make good value bets on the river. The beauty of the power of position is that even if you don't really understand its benefits, you will automatically perform better in position than out of position. Position is a magic that works even on those who don't realize it.