The lights on the left are for the fencer on the left, and vice versa. Often, even though a touch is awarded by the lights, it is not awarded by the referee, because of complicated rules and situations determined by the referee. The official makes a broad gesture indicating a touch. The foil is the modern version of the small sword, and the rules are intended to simulate a duel to the death. Therefore, the torso is a valid target front and back due to the presence of the vital organs.
Touches have to be made with at least a pound of pressure to count.
The arms, head and legs are foul. The defender now takes over the right-of way until a hit or a parry. Sawing or whacking your opponent with the side of the blade can be painful, but never scores any points. It evolved during the 1800s when the small sword ceased to be worn. The target is the whole body, including clothing and equipment.