Rook Fork
A fork or double attack creates two threats at the same time, so the opponent cannot answer both.
What to look for
Look for checks or attacks that hit the king, queen, rook, loose pieces, or mate threats at once.
Recognize the mechanism
Look across the rank and up the file from a candidate rook square. The perpendicular lines can create two threats, sometimes using a check to limit the reply. Check all blockers before comparing targets.
Common practical mistake
A defended destination or an intervening piece can ruin a geometrically attractive fork. Calculate the capture and recapture sequence.
Training goal
Train your eye to find moves with two purposes.