Perceiving and being in the wa is an important concept in my martial arts system, Mo Duk Pai kung fu. As we understand it, wa is the existing state of harmony in a given situation, encompassing all things. Being in the wa means being aware of the physical environment, social norms, and moods and attitudes of participants. When one is in the wa, one can act in a way to preserve or increase harmony. To the American mind, it sounds a little like "go with the flow", but is a more active and aware state than that. It is a intuitive state that can be cultivated with practice.
My sifu likes to illustrate wa with the example of funerary practices in Ireland versus in the United States. At an Irish wake it is perfectly acceptable to sing and dance, but at most funerals in the United States that would be grossly unacceptable.