Definition of out (of) position
What is meant by "out of position" is when you talk first on the flop. Talking last is talking 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, regardless of the action. But an out-of-position position can 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. However, if all players fold to the raise except the big blind, now the UTG player will be in position on the BB.
Out of position after the flop
Imagine that 5 players see the flop including the button. Then there will not be players in position and players out of position. There will only be 4 players out of position and one player in position, the button. Obviously, we can always say that the player on the cutoff has a better position than the player in the small blind, we can also say that the player on the cutoff has position over the player in the small blind, but this player will not be officially in position because he will always talk before the button.