The term Kung Fu is the transliteration for the Chinese term “工夫 or 功夫.” The English term mainly refers to a style of traditional Chinese martial art, especially Shaolin Kung Fu, meaning Shaolin style martial art.
The original Chinese term means a lot more:
In traditional Chinese martial art community, 功夫 mainly means 2 things:
功夫 takes a lot of time and effort to obtain and accumulate, therefore it is considered the most important part of martial art training. 练功 usually involves practice a single, simple move or a stance repeatedly for a long time. Masters usually tell their pupils to stay on a horse stance for hours or to practice one simple punch hundreds of times. When a martial artist says he is 练功, he is saying he is practicing the fundamentals.
功夫 is the simple plain fundamentals that is behind all the fancy moves and forms.
A martial artist practices the fundamentals since the first day of his martial art training to the last day of his life. That reflects the importance of 功夫.