OTB
OTB is short for 'on the button'. It is used in hand histories and discussions to describe the player in the button seat.
The simple explanation
When people write, 'I raised in the CO and the player OTB called', they mean that the player on the button called. The button is the best position.
A closer look
Abbreviations such as OTB, CO, UTG, SB and BB are standard in hand histories. They make descriptions short. OTB is usually written for the button, but 'BTN' is also common. The player OTB acts last after the flop, which gives him a large positional advantage.
A practical example
A forum post says: 'Hero raises in the CO, and the player OTB calls.'
Full explanation
OTB is short for ‘on the button’. It is used in hand histories and discussions to describe the player in the button seat.
OTB means on the button.
It is used in hand histories.
The button is the best position.
BTN is another abbreviation.
Alternative spelling: On the Button