Definition of OOP
OOP means "Out Of Poker" (out of position in French). What is meant by "hors de position" is when one speaks first to flop. Speaking last is speaking in position. preflop, several positions are considered out of position. UTG, SB, BB are positions considered out of position. The button will always be in position, no matter what action is taken. But a position out of position may end up in position if the player it is playing against has a worse position. For example, a player opens in UTG position. This position is considered out of position. On the other hand, if all the players lie down facing the throw except the big blind, now the UTG player will be in position on the BB.
OOP after the flop
Imagine that 5 players see the flop with the button. There will then be no players in position and no players out of position. There will only be 4 players out of position and one player in position, the button. Of course, we can always say that the player on the cutoff has a better position than the player on the small blind, we can also say that the player on the cutoff has a position on the player in the small blind, but this player will not be officially in position because he will always speak before the button.