A three-bet is a poker term indicating a raise against an opponent who has already raised. 

Back in the day, when you needed an aircraft hangar to house a computer, a three-bet would have always meant either pocket aces or pocket kings but, these days, players can three-bet with ranges wider than the Grand Canyon.

When you three-bet in position, it can be a highly profitable play, and one that is extremely difficult to counter for the player out of position. Even if players have been paying attention, and understand that you have a wide three-betting range, it is still very difficult to counter. 

What usually happens is that players adjust by widening their stacking off range, meaning you can fold your 9BB bet, or call and be up against a much weaker range.

The introduction of the light three-bet has been a revelation to the game of poker. It has increased pot size and variance, thus introducing a lot more fizz and excitement.

But adjusting to three-betting – as difficult as it may be – is no different than making adjustments for any area of your poker game; it is necessary and very dependant on the type of opponent you are facing. 

Until you become a skilled poker practitioner, playing in the WSOP Qualifiers, it is sensible to have a tight three-betting range. Just choose the hands you are willing to stack off with and go with them. 

Then when you build a stronger foundation, you can start to incorporate some bluffs into your range. But there is no rush. You cannot win a game of poker in just one hand, so be patient and bide your time, even against the most aggressive of three-betting opponents.