There is more than one meaning to the term break especially when it comes to using it in poker.
The first one is during a game where a player decides to break up a made hand that s/he has, in order to try and get something better. This kind of a situation normally occurs only in draw poker where a player has the option of throwing away cards from an existing hand. If a player has, say, a hand that has J-J-Q-K-A; then if the player decides to throw away one of the pair of Jacks in order to hope for a straight, then this action is known as a break.
The player simply broke his existing hand of a pair of Jacks in order to get a higher ranked hand. Whether the player ends up with a higher ranked hand or not is immaterial as the action of breaking the original hand is the action that is called the break.
The other form of break occurs when players take a break from the game for whatever reason, be it a toilet break, to end the session of play or to simply call it a day.