A discovered attack is one that takes place by the removal of a piece blocking an attacker. For instance, if the black bishop is between the black rook and the white queen, once the black bishop is moved, an attack is 'discovered' against the queen. The bishop may place the white king in check forcing the exchange or loss of the queen for a lesser piece, it may take a white pawn or piece without retaliation because of the attack on the queen, or it may simply take up a strategic location on the board. The discovered attack is also very effective when it is against the king (discovered check), and it is involved in the double check which is perhaps a topic for another day.
In life, as in chess, a discovered attack (or check) is a result of being caught unaware or unprepared. Perhaps, you took note of the threat earlier as positional play developed, but at some point whether through the opponent's strategic play or through your own error, your pieces were left exposed. A discovered attack may come in the form of a late night party causing you to want to sleep in or call in sick instead of waking up for your early class or going to work.
