What is a Discovered Attack?

A discovered attack occurs when one of your pieces moves out of the way and reveals an attack from a piece behind it. For example, as shown in the diagram on the left, your rook is lined up with your opponent’s queen, but one of your own pieces is blocking it. When that blocking piece moves, the rook suddenly attacks the queen. The attack was hidden, and now it has been discovered.

Definition:

Discovered attacks are powerful because they catch your opponent off guard and could create two threats at once. The piece that moves can make a threat of its own, while the revealed piece also attacks something important. This puts your opponent under pressure and can help you win material or even deliver checkmate. Learning to line up your pieces and look for hidden attacks will help you find discovered attacks and nice tactics during real games.

Why discovered attacks are powerful?