When a person has developed a “Kung Fu” 功夫 he/she has a skill level that very few others have. The use of the expression “Kung Fu” can refer to any skill where repetition and time develop a nameless quality and ability in a person. A level that others cannot achieve without enormous effort and sacrifice. This could be opera performance, gymnastics, or even cooking. It most often refers the the Chinese Martial Arts in an umbrella type term that includes all styles and systems.
The expression, Kung Fu 功夫 , is derived from the Cantonese dialect and was made popular through Chinese Martial Arts movies. The romanisation is the old method used in Hong Kong prior to 1997.
Sadly, today, very few Chinese Martial Arts practitioners exhibit any level of “Kung Fu”. Most tangible skills are too difficult to master and modern practitioners prefer to practice forms where no actual warrior skill is required. When applied to Yin Fa, the Midnight Thief should master such skills as, running roofs and walls (similar to today’s parkour), Fei Biao (hand thrown projectiles), the Chinese bow, the flying claw and many others.