The one inch punch is a punching technique from Kung Fu performed at very close (0-6 inches) range.
It is commonly believed that the One inch punch skill comes only from the Wing Chun system of Kung Fu, however, it is present in many styles of Southern Chinese martial arts. As a general rule, Southern Chinese martial arts rely mostly on hand techniques from very close quarters (as opposed to Northern Chinese martial arts which focus more on kicking techniques from medium to long distances). Because the Southern styles martial artists were often fighting nose-to-nose with their opponents, they had to learn a way to deal out punishing blows even while almost touching their target.
Please read more at Wikipedia - One Inch Punch.
