Definition of flashed
What is meant by "flashed" is a card that has been flashed. This can happen for a variety of reasons. A flashed card or cards are cards that should have remained hidden but for one reason or another have been revealed to one or more players at the table. For example, let's say there are four players involved in a hand on the flop. One player bets, one player calls and one player decides to fold. As he folds, he throws his cards into the muck and a card is accidentally flashed, i.e. it ends up face up, visible to one or more players.
What to do when a card is flashed?
Here, when one or more cards are flashed, the dealer steps in and makes sure that all players still in the hand can see the card that has been flashed so as not to give an unfair advantage to any player. This card will be left face up on the table, visible to all. When a player throws his cards into the muck in this way and one of his cards is flashed, there is no problem if it is the first time, but if it becomes a habit, the player in question will get a warning.