Definition of bubble
The bubble to poker is only present in tournaments (or sit'n'gos). The bubble is the phenomenon that occurs just before the paid seats. For example, in a tournament, 1000 players register. This tournament offers 100 paid seats according to a predetermined structure. The first paid place (the 100th position) will give about 150% of its entry cost. So, if the tournament had a buy-in cost of 100 euros, finishing 100th would give you about 150 euros. Finishing 101st would give you 0 euros. From say 110 players remaining in the tournament, there will be a phenomenon of bubble where the majority of players will be more cautious and conservative in accessing the paid seats. In short, the bubble is the moment just before the paid places. When this stage is over, the bubble is said to be exhausted.
The philosophy of bubble
There will generally be 2 philosophies of the bubble, therefore, 2 types of players with 2 different visions. The first type of player, more aggressive, will say that since the players are more conservative when approaching the paid seats (the bubble), he will be more aggressive and bluffing to take advantage of this passivity. He is the one who will play the whole for the sake of the whole. And there is the 2nd type of player who will be more conservative and take the least possible risks to get to the paid places.